Multiphoton photosensitization system

ABSTRACT

A method of multiphoton photosensitizing a photoreactive composition comprises irradiating the composition with light sufficient to cause simultaneous absorption of at least two photons, thereby inducing at least one acid- or radical-initiated chemical reaction where the composition is exposed to the light. The composition comprises: (a) at least one reactive species that is capable of undergoing such reaction; and (b) at least one multi-component, multiphoton photoinitiator system.

STATEMENT OF PRIORITY

This application claims the priority of U.S. Provisional Application No.60/211,703 filed Jun. 15, 2000, the contents of which are herebyincorporated by reference.

FIELD

This invention relates to multiphoton methods of photo-inducing chemicalreactions.

BACKGROUND

Molecular two-photon absorption was predicted by Goppert-Mayer in 1931.Upon the invention of pulsed ruby lasers in 1960, experimentalobservation of two-photon absorption became a reality. Subsequently,two-photon excitation has found application in biology and optical datastorage, as well as in other fields.

There are two key differences between two-photon induced photoprocessesand single-photon induced processes. Whereas single-photon absorptionscales linearly with the intensity of the incident radiation, two-photonabsorption scales quadratically. Higher-order absorptions scale with arelated higher power of incident intensity. As a result, it is possibleto perform multiphoton processes with three-dimensional spatialresolution. Also, because multiphoton processes involve the simultaneousabsorption of two or more photons, the absorbing chromophore is excitedwith a number of photons whose total energy equals the energy of anelectronic excited state of the multiphoton photosensitizer that isutilized, even though each photon individually has insufficient energyto excite the chromophore. Because the exciting light is not attenuatedby single-photon absorption within a curable matrix or material, it ispossible to selectively excite molecules at a greater depth within amaterial than would be possible via single-photon excitation by use of abeam that is focused to that depth in the material. These two phenomenaalso apply, for example, to excitation within tissue or other biologicalmaterials.

Major benefits have been achieved by applying multiphoton absorption tothe areas of photocuring and microfabrication. For example, inmultiphoton lithography or stereolithography, the nonlinear scaling ofmultiphoton absorption with intensity has provided the ability to writefeatures having a size that is less than the diffraction limit of thelight utilized, as well as the ability to write features in threedimensions (which is also of interest for holography). Such work hasbeen limited, however, to slow writing speeds and high laser powers, dueto the low photosensitivities of current multiphoton-activatable,photoreactive compositions. Thus, we recognize that there is a need formethods of improving the photosensitivities of such compositions.

SUMMARY

The present invention provides a method of multiphoton photosensitizinga photoreactive composition. The method comprises irradiating(preferably, pulse irradiating) the composition with light sufficient tocause simultaneous absorption of at least two photons, thereby inducingat least one acid- or radical-initiated chemical reaction where thecomposition is exposed to the light. The photoreactive compositioncomprises: (a) at least one reactive species that is capable ofundergoing an acid- or radical-initiated chemical reaction (preferably,a curable species; more preferably, a curable species selected from thegroup consisting of monomers, oligomers, and reactive polymers); and (b)at least one multiphoton photoinitiator system.

The multiphoton photoinitiator system comprises photochemicallyeffective amounts of (1) at least one multiphoton photosensitizer thatis capable of simultaneously absorbing at least two photons and that hasa two-photon absorption cross-section greater than that of fluorescein(generally, greater than about 50×10⁻⁵⁰ cm⁴ sec/photon, as measured bythe method described by C. Xu and W. W. Webb in J. Opt. Soc. Am. B, 13,481 (1996)); (2) optionally, at least one electron donor compounddifferent from the multiphoton photosensitizer and capable of donatingan electron to an electronic excited state of the photosensitizer(preferably, an electron donor compound having an oxidation potentialthat is greater than zero and less than or equal to that ofp-dimethoxybenzene); and (3) at least one photoinitiator that is capableof being photosensitized by accepting an electron from an electronicexcited state of the photosensitizer, resulting in the formation of atleast one free radical and/or acid (preferably, a photoinitiatorselected from the group consisting of iodonium salts, sulfonium salts,diazonium salts, azinium salts, chloromethylated triazines, andtriarylimidazolyl dimers); with the proviso that the multiphotonphotoinitiator system comprises at least one electron donor compoundwhenever the photoreactive composition comprises at least one reactivespecies that is capable of undergoing an acid-initiated chemicalreaction and that is either a curable species or a non-curable, reactivepolymer.

The method of the invention provides enhanced multiphotonphotosensitivity by combining (in photochemically-effective amounts)multiphoton photosensitizers having relatively large two-photonabsorption cross sections (compared to those of many commonly-availabledyes) with photoinitiators that are further enhanced by electron donorsso as to efficiently form reaction-initiating species (radicals, acids,etc.). The increased sensitivity of the method of the invention providesutility by, for example, allowing rapid fabrication of three-dimensionalstructures and permitting the use of lower peak intensity lasers(including, for example, robust industrial lasers such as nanosecond andpicosecond Nd:YAG lasers) for exposure.

In another aspect, this invention also provides a novelmultiphoton-activatable, photoreactive composition comprising (a) atleast one reactive species that is capable of undergoing an acid- orradical-initiated chemical reaction other than a curing reaction; and(b) at least one multiphoton photoinitiator system comprisingphotochemically effective amounts of (1) at least one multiphotonphotosensitizer that is capable of simultaneously absorbing at least twophotons, (2) at least one electron donor compound that is different fromthe multiphoton photosensitizer, different from the reactive species,and capable of donating an electron to an electronic excited state ofthe photosensitizer, and (3) at least one photoinitiator that is capableof being photosensitized by accepting an electron from an electronicexcited state of the photosensitizer, resulting in the formation of atleast one free radical and/or acid; with the proviso that thecomposition contains no curable species.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood with regard to the followingdescription, appended claims, and accompanying drawings, wherein:

FIG. 1 is a plot of threshold write speed (in micrometers per second)versus power (in milliwatts) for the coated films of Example 7, infra.

DETAILED DESCRIPTION

Definitions

As used in this patent application:

“multiphoton absorption” means simultaneous absorption of two or morephotons to reach a reactive, electronic excited state that isenergetically inaccessible by the absorption of a single photon of thesame energy;

“simultaneous” means two events that occur within the period of 10⁻¹⁴seconds or less;

“electronic excited state” means an electronic state of a molecule thatis higher in energy than the molecule's electronic ground state, that isaccessible via absorption of electromagnetic radiation, and that has alifetime greater than 10⁻¹³ seconds;

“cure” means to effect polymerization and/or to effect crosslinking;

“optical system” means a system for controlling light, the systemincluding at least one element chosen from refractive optical elementssuch as lenses, reflective optical elements such as mirrors, anddiffractive optical elements such as gratings. Optical elements shallalso include diffusers, waveguides, and other elements known in theoptical arts;

“three-dimensional light pattern” means an optical image wherein thelight energy distribution resides in a volume or in multiple planes andnot in a single plane;

“exposure system” means an optical system plus a light source;

“sufficient light” means light of sufficient intensity and appropriatewavelength to effect multiphoton absorption;

“photosensitizer” means a molecule that lowers the energy required toactivate a photoinitiator by absorbing light of lower energy than isrequired by the photoinitiator for activation and interacting with thephotoinitiator to produce a photoinitiating species therefrom; and

“photochemically effective amounts” (of the components of thephotoinitiator system) means amounts sufficient to enable the reactivespecies to undergo at least partial reaction under the selected exposureconditions (as evidenced, for example, by a change in density,viscosity, color, pH, refractive index, or other physical or chemicalproperty).

Reactive Species

Reactive species suitable for use in the photoreactive compositionsinclude both curable and non-curable species. Curable species aregenerally preferred and include, for example, addition-polymerizablemonomers and oligomers and addition-crosslinkable polymers (such asfree-radically polymerizable or crosslinkable ethylenically-unsaturatedspecies including, for example, acrylates, methacrylates, and certainvinyl compounds such as styrenes), as well as cationically-polymerizablemonomers and oligomers and cationically-crosslinkable polymers (whichspecies are most commonly acid-initiated and which include, for example,epoxies, vinyl ethers, cyanate esters, etc.), and the like, and mixturesthereof.

Suitable ethylenically-unsaturated species are described, for example,by Palazzotto et al. in U.S. Pat. No. 5,545,676 at column 1, line 65,through column 2, line 26, and include mono-, di-, and poly-acrylatesand methacrylates (for example, methyl acrylate, methyl methacrylate,ethyl acrylate, isopropyl methacrylate, n-hexyl acrylate, stearylacrylate, allyl acrylate, glycerol diacrylate, glycerol triacrylate,ethyleneglycol diacrylate, diethyleneglycol diacrylate,triethyleneglycol dimethacrylate,1,3-propanediol diacrylate,1,3-propanediol dimethacrylate, trimethylolpropane triacrylate,1,2,4-butanetriol trimethacrylate, 1,4-cyclohexanediol diacrylate,pentaerythritol triacrylate, pentaerythritol tetraacrylate,pentaerythritol tetramethacrylate, sorbitol hexacrylate,bis[1-(2-acryloxy)]-p-ethoxyphenyldimethylmethane,bis[1-(3-acryloxy-2-hydroxy)]-p-propoxyphenyldimethylmethane,trishydroxyethyl-isocyanurate trimethacrylate, the bis-acrylates andbis-methacrylates of polyethylene glycols of molecular weight about200-500, copolymerizable mixtures of acrylated monomers such as those ofU.S. Pat. No. 4,652,274, and acrylated oligomers such as those of U.S.Pat. No. 4,642,126); unsaturated amides (for example, methylenebis-acrylamide, methylene bis-methacrylamide, 1,6-hexamethylenebis-acrylamide, diethylene triamine tris-acrylamide andbeta-methacrylaminoethyl methacrylate); vinyl compounds (for example,styrene, diallyl phthalate, divinyl succinate, divinyl adipate, anddivinyl phthalate); and the like; and mixtures thereof. Suitablereactive polymers include polymers with pendant (meth)acrylate groups,for example, having from 1 to about 50 (meth)acrylate groups per polymerchain. Examples of such polymers include aromatic acid (meth)acrylatehalf ester resins such as Sarbox™ resins available from Sartomer (forexample, Sarbox™ 400, 401, 402, 404, and 405). Other useful reactivepolymers curable by free radical chemistry include those polymers thathave a hydrocarbyl backbone and pendant peptide groups withfree-radically polymerizable functionality attached thereto, such asthose described in U.S. Pat. No. 5,235,015 (Ali et al.). Mixtures of twoor more monomers, oligomers, and/or reactive polymers can be used ifdesired. Preferred ethylenically-unsaturated species include acrylates,aromatic acid (meth)acrylate half ester resins, and polymers that have ahydrocarbyl backbone and pendant peptide groups with free-radicallypolymerizable functionality attached thereto.

Suitable cationically-reactive species are described, for example, byOxman et al. in U.S. Pat. Nos. 5,998,495 and 6,025,406 and include epoxyresins. Such materials, broadly called epoxides, include monomeric epoxycompounds and epoxides of the polymeric type and can be aliphatic,alicyclic, aromatic, or heterocyclic. These materials generally have, onthe average, at least 1 polymerizable epoxy group per molecule(preferably, at least about 1.5 and, more preferably, at least about 2).The polymeric epoxides include linear polymers having terminal epoxygroups (for example, a diglycidyl ether of a polyoxyalkylene glycol),polymers having skeletal oxirane units (for example, polybutadienepolyepoxide), and polymers having pendant epoxy groups (for example, aglycidyl methacrylate polymer or copolymer). The epoxides can be purecompounds or can be mixtures of compounds containing one, two, or moreepoxy groups per molecule. These epoxy-containing materials can varygreatly in the nature of their backbone and substituent groups. Forexample, the backbone can be of any type and substituent groups thereoncan be any group that does not substantially interfere with cationiccure at room temperature. Illustrative of permissible substituent groupsinclude halogens, ester groups, ethers, sulfonate groups, siloxanegroups, nitro groups, phosphate groups, and the like. The molecularweight of the epoxy-containing materials can vary from about 58 to about100,000 or more.

Useful epoxy-containing materials include those which containcyclohexene oxide groups such as epoxycyclohexanecarboxylates, typifiedby 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate,3,4-epoxy-2-methylcyclohexylmethyl-3,4-epoxy-2-methylcyclohexanecarboxylate, and bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate. A moredetailed list of useful epoxides of this nature is set forth in U.S.Pat. No. 3,117,099.

Other epoxy-containing materials that are useful include glycidyl ethermonomers of the formula

where R′ is alkyl or aryl and n is an integer of 1 to 6. Examples areglycidyl ethers of polyhydric phenols obtained by reacting a polyhydricphenol with an excess of a chlorohydrin such as epichlorohydrin (forexample, the diglycidyl ether of2,2-bis-(2,3-epoxypropoxyphenol)-propane). Additional examples ofepoxides of this type are described in U.S. Pat. No. 3,018,262, and inHandbook of Epoxy Resins, Lee and Neville, McGraw-Hill Book Co., NewYork (1967).

Numerous commercially available epoxy resins can also be utilized. Inparticular, epoxides that are readily available include octadecyleneoxide, epichlorohydrin, styrene oxide, vinyl cyclohexene oxide,glycidol, glycidylmethacrylate, diglycidyl ethers of Bisphenol A (forexample, those available under the trade designations Epon™ 828, Epon™825, Epon™ 1040, and Epon™ 1010 from Resolution Performance Products,formerly Shell Chemical Co., as well as DER™-331, DER™-332, and DER™-334from Dow Chemical Co.), vinylcyclohexene dioxide (for example, ERL-4206from Union Carbide Corp.),3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexene carboxylate (for example,ERL-4221 or Cyracure™ UVR 6110 or UVR 6105 from Union Carbide Corp.),3,4-epoxy-6-methylcyclohexylmethyl-3,4-epoxy-4-methyl-cyclohexenecarboxylate (for example, ERL-4201 from Union Carbide Corp.),bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate (for example. ERL-4289from Union Carbide Corp.), bis(2,3-epoxycyclopentyl) ether (for example,ERL-0400 from Union Carbide Corp.), aliphatic epoxy modified frompolypropylene glycol (for example, ERL-4050 and ERL-4052 from UnionCarbide Corp.), dipentene dioxide (for example, ERL-4269 from UnionCarbide Corp.), epoxidized polybutadiene (for example. Oxiron™ 2001 fromFMC Corp.), silicone resin containing epoxy functionality, flameretardant epoxy resins (for example, DER™-580, a brominated bisphenoltype epoxy resin available from Dow Chemical Co.) 1,4-butanedioldiglycidyl ether of phenolformaldehyde novolak (for example, DEN™-431and DEN™-438 from Dow Chemical Co.), resorcinol diglycidyl ether (forexample, Kopoxite™ from Koppers Company, Inc.),bis(3,4-epoxycyclohexyl)adipate (for example, ERL-4299 or UVR-6128, fromUnion Carbide Corp.),2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy)cyclohexane-meta-dioxane (forexample, ERL-4234 from Union Carbide Corp.), vinylcyclohexene monoxide1,2-epoxyhexadecane (for example, UVR-6216 from Union Carbide Corp.),alkyl glycidyl ethers such as alkyl C₈-C₁₀ glycidyl ether (for example,Heloxy™ Modifier 7 from Resolution Performance Products), alkyl C₁₂-C₁₄glycidyl ether (for example, Heloxy™ Modifier 8 from ResolutionPerformance Products), butyl glycidyl ether (for example, Heloxy™Modifier 61 from Resolution Performance Products), cresyl glycidyl ether(for example, Heloxy™ Modifier 62 from Resolution Performance Products),p-tert-butylphenyl glycidyl ether (for example, Heloxy™ Modifier 65 fromResolution Performance Products), polyfunctional glycidyl ethers such asdiglycidyl ether of 1,4-butanediol (for example, Heloxy™ Modifier 67from Resolution Performance Products), diglycidyl ether of neopentylglycol (for example, Heloxy™ Modifier 68 from Resolution PerformanceProducts), diglycidyl ether of cyclohexanedimethanol (for example,Heloxy™ Modifier 107 from Resolution Performance Products), trimethylolethane triglycidyl ether (for example, Heloxy™ Modifier 44 fromResolution Performance Products), trimethylol propane triglycidyl ether(for example, Heloxy™ Modifier 48 from Resolution Performance Products),polyglycidyl ether of an aliphatic polyol (for example, Heloxy™ Modifier84 from Resolution Performance Products), polyglycol diepoxide (forexample, Heloxy™ Modifier 32 from Resolution Performance Products),bisphenol F epoxides (for example, Epon™-1138 or GY-281 from Ciba-GeigyCorp.), and 9,9-bis[4-(2,3-epoxypropoxy)-phenyl]fluorenone (for example,Epon™ 1079 from Resolution Performance Products).

Other useful epoxy resins comprise copolymers of acrylic acid esters ofglycidol (such as glycidylacrylate and glycidylmethacrylate) with one ormore copolymerizable vinyl compounds. Examples of such copolymers are1:1 styrene-glycidylmethacrylate, 1:1methylmethacrylate-glycidylacrylate, and a 62.5:24:13.5methylmethacrylate-ethyl acrylate-glycidylmethacrylate. Other usefulepoxy resins are well known and contain such epoxides asepichlorohydrins, alkylene oxides (for example, propylene oxide),styrene oxide, alkenyl oxides (for example, butadiene oxide), andglycidyl esters (for example, ethyl glycidate).

Useful epoxy-functional polymers include epoxy-functional silicones suchas those described in U.S. Pat. No. 4,279,717 (Eckberg), which arecommercially available from the General Electric Company. These arepolydimethylsiloxanes in which 1-20 mole % of the silicon atoms havebeen substituted with epoxyalkyl groups (preferably, epoxycyclohexylethyl, as described in U.S. Pat. No. 5,753,346 (Kessel)).

Blends of various epoxy-containing materials can also be utilized. Suchblends can comprise two or more weight average molecular weightdistributions of epoxy-containing compounds (such as low molecularweight (below 200), intermediate molecular weight (about 200 to 10,000),and higher molecular weight (above about 10,000)). Alternatively oradditionally, the epoxy resin can contain a blend of epoxy-containingmaterials having different chemical natures (such as aliphatic andaromatic) or functionalities (such as polar and non-polar). Othercationically-reactive polymers (such as vinyl ethers and the like) canadditionally be incorporated, if desired.

Preferred epoxies include aromatic glycidyl epoxies (such as the Epon™resins available from Resolution Performance Products) andcycloaliphatic epoxies (such as ERL-4221 and ERL-4299 available fromUnion Carbide).

Suitable cationally-reactive species also include vinyl ether monomers,oligomers, and reactive polymers (for example, methyl vinyl ether, ethylvinyl ether, tert-butyl vinyl ether, isobutyl vinyl ether,triethyleneglycol divinyl ether (Rapi-Cure™ DVE-3, available fromInternational Specialty Products, Wayne, N.J.), trimethylolpropanetrivinyl ether (TMPTVE, available from BASF Corp., Mount Olive, N.J.),and the Vectomer™ divinyl ether resins from Allied Signal (for example,Vectomer™ 2010, Vectomer™ 2020, Vectomer™ 4010, and Vectomer™ 4020 andtheir equivalents available from other manufacturers)), and mixturesthereof. Blends (in any proportion) of one or more vinyl ether resinsand/or one or more epoxy resins can also be utilized.Polyhydroxy-functional materials (such as those described, for example,in U.S. Pat. No. 5,856,373 (Kaisaki et al.)) can also be utilized incombination with epoxy- and/or vinyl ether-functional materials.

Non-curable species include, for example, reactive polymers whosesolubility can be increased upon acid- or radical-induced reaction. Suchreactive polymers include, for example, aqueous insoluble polymersbearing ester groups that can be converted by photogenerated acid toaqueous soluble acid groups (for example,poly(4-tert-butoxycarbonyloxystyrene). Non-curable species also includethe chemically-amplified photoresists described by R. D. Allen, G. M.Wallraff, W. D. Hinsberg, and L. L. Simpson in “High Performance AcrylicPolymers for Chemically Amplified Photoresist Applications,” J. Vac.Sci. Technol. B, 9, 3357 (1991). The chemically-amplified photoresistconcept is now widely used for microchip manufacturing, especially withsub-0.5 micron (or even sub-0.2 micron) features. In such photoresistsystems, catalytic species (typically hydrogen ions) can be generated byirradiation, which induces a cascade of chemical reactions. This cascadeoccurs when hydrogen ions initiate reactions that generate more hydrogenions or other acidic species, thereby amplifying reaction rate. Examplesof typical acid-catalyzed chemically-amplified photoresist systemsinclude deprotection (for example, t-butoxycarbonyloxystyrene resists asdescribed in U.S. Pat. No. 4,491,628, tetrahydropyran (THP)methacrylate-based materials, THP-phenolic materials such as thosedescribed in U.S. Pat. No. 3,779,778, t-butyl methacrylate-basedmaterials such as those described by R. D Allen et al. in Proc. SPIE2438, 474 (1995), and the like); depolymerization (for example,polyphthalaldehyde-based materials); and rearrangement (for example,materials based on the pinacol rearrangements).

Useful non-curable species also include leuco dyes, which tend to becolorless until they are oxidized by acid generated by the multiphotonphotoinitiator system, and which, once oxidized, exhibit a visiblecolor. (Oxidized dyes are colored by virtue of their absorbance of lightin the visible portion of the electromagnetic spectrum (approximately400-700 nm).) Leuco dyes useful in the present invention are those thatare reactive or oxidizable under moderate oxidizing conditions and yetthat are not so reactive as to oxidize under common environmentalconditions. There are many such chemical classes of leuco dyes known tothe imaging chemist.

Leuco dyes useful as reactive species in the present invention includeacrylated leuco azine, phenoxazine, and phenothiazine, which can, inpart, be represented by the structural formula:

wherein X is selected from O, S, and —N—R¹¹, with S being preferred; R¹and R² are independently selected from H and alkyl groups of 1 to about4 carbon atoms; R³, R⁴, R⁶, and R⁷ are independently selected from H andalkyl groups of 1 to about 4 carbon atoms, preferably methyl; R⁵ isselected from alkyl groups of 1 to about 16 carbon atoms, alkoxy groupsof 1 to about 16 carbon atoms, and aryl groups of up to about 16 carbonatoms; R⁸ is selected from —N(R¹)(R²), H, alkyl groups of 1 to about 4carbon atoms, wherein R¹ and R² are independently selected and definedas above; R⁹ and R¹⁰ are independently selected from H and alkyl groupsof 1 to about 4 carbon atoms; and R¹¹ is selected from alkyl groups of 1to about 4 carbon atoms and aryl groups of up to about 11 carbon atoms(preferably, phenyl groups). The following compounds are examples ofthis type of leuco dye:

Other useful leuco dyes include, but are not limited to, Leuco CrystalViolet (4,4′,4″-methylidynetris-(N,N-diethylaniline)), Leuco MalachiteGreen (p,p′-benzylidenebis-(N,N-dimethylaniline)), Leuco AtacrylOrange-LGM (Color Index Basic Orange 21, Comp. No. 48035 (a Fischer'sbase type compound)) having the structure

Leuco Atacryl Brilliant Red-4G (Color Index Basic Red 14) having thestructure

Leuco Atacryl Yellow-R (Color Index Basic Yellow 11, Comp. No. 48055)having the structure

Leuco Ethyl Violet (4,4′,4″-methylidynetris-(N,N-diethylaniline), LeucoVictoria Blu-BGO (Color Index Basic Blue 728a, Comp. No. 44040;4,4′-methylidynebis-(N,N,-dimethylaniline)-4-(N-ethyl-1-napthalamine)),and Leuco Atlantic Fuchsine Crude (4,4′,4″-methylidynetris-aniline).

The leuco dye(s) can generally be present at levels of at least about0.01% by weight of the total weight of a light sensitive layer(preferably, at least about 0.3% by weight; more preferably, at leastabout 1% by weight; most preferably, at least about 2% to 10% or more byweight). Other materials such as binders, plasticizers, stabilizers,surfactants, antistatic agents, coating aids, lubricants, fillers, andthe like can also be present in the light sensitive layer.

If desired, mixtures of different types of reactive species can beutilized in the photoreactive compositions. For example, mixtures offree-radically-reactive species and cationically-reactive species,mixtures of curable species and non-curable species, and so forth, arealso useful.

Photoinitiator System

(1) Multiphoton Photosensitizers

Multiphoton photosensitizers suitable for use in the multiphotonphotoinitiator system of the photoreactive compositions are those thatare capable of simultaneously absorbing at least two photons whenexposed to sufficient light and that have a two-photon absorptioncross-section greater than that of fluorescein (that is, greater thanthat of 3′,6′-dihydroxyspiro[isobenzofuran-1(3H), 9′-[9H]xanthen]3-one).Generally, the cross-section can be greater than about 50×10⁻⁵⁰ cm⁴sec/photon, as measured by the method described by C. Xu and W. W. Webbin J. Opt. Soc. Am. B, 13, 481 (1996) (which is referenced by Marder andPerry et al. in International Publication No. WO 98/21521 at page 85,lines 18-22).

This method involves the comparison (under identical excitationintensity and photosensitizer concentration conditions) of thetwo-photon fluorescence intensity of the photosensitizer with that of areference compound. The reference compound can be selected to match asclosely as possible the spectral range covered by the photosensitizerabsorption and fluorescence. In one possible experimental set-up, anexcitation beam can be split into two arms, with 50% of the excitationintensity going to the photosensitizer and 50% to the referencecompound. The relative fluorescence intensity of the photosensitizerwith respect to the reference compound can then be measured using twophotomultiplier tubes or other calibrated detector. Finally, thefluorescence quantum efficiency of both compounds can be measured underone-photon excitation.

Methods of determining fluorescence and phosphorescence quantum yieldsare well-known in the art. Typically, the area under the fluorescence(or phosphorescence) spectrum of a compound of interest is compared withthe area under the fluorescence (or phosphorescence) spectrum of astandard luminescent compound having a known fluorescence (orphosphorescence) quantum yield, and appropriate corrections are made(which take into account, for example, the optical density of thecomposition at the excitation wavelength, the geometry of thefluorescence detection apparatus, the differences in the emissionwavelengths, and the response of the detector to different wavelengths).Standard methods are described, for example, by I. B. Berlman inHandbook of Fluorescence Spectra of Aromatic Molecules, Second Edition,pages 24-27, Academic Press, New York (1971); by J. N. Demas and G. A.Crosby in J. Phys. Chem. 75, 991-1024 (1971); and by J. V. Morris, M. A.Mahoney, and J. R. Huber in J. Phys. Chem. 80, 969-974 (1976).

Assuming that the emitting state is the same under one- and two-photonexcitation (a common assumption), the two-photon absorptioncross-section of the photosensitizer, (δ_(sam)), is equal to δ_(ref) K(I_(sam)/I_(ref))(Φ_(sam)/Φ_(ref)), wherein δ_(ref) is the two-photonabsorption cross-section of the reference compound, I_(sam) thefluorescence intensity of the photosensitizer, I_(ref) is thefluorescence intensity of the reference compound, Φ_(sam) is thefluorescence quantum efficiency of the photosensitizer, Φ_(ref) is thefluorescence quantum efficiency of the reference compound, and K is acorrection factor to account for slight differences in the optical pathand response of the two detectors. K can be determined by measuring theresponse with the same photosensitizer in both the sample and referencearms. To ensure a valid measurement, the clear quadratic dependence ofthe two-photon fluorescence intensity on excitation power can beconfirmed, and relatively low concentrations of both the photosensitizerand the reference compound can be utilized (to avoid fluorescencereabsorption and photosensitizer aggregration effects).

When the photosensitizer is not fluorescent, the yield of electronicexcited states can to be measured and compared with a known standard. Inaddition to the above-described method of determining fluorescenceyield, various methods of measuring excited state yield are known(including, for example, transient absorbance, phosphorescence yield,photoproduct formation or disappearance of photosensitizer (fromphotoreaction), and the like).

Preferably, the two-photon absorption cross-section of thephotosensitizer is greater than about 1.5 times that of fluorescein (or,alternatively, greater than about 75×10⁻⁵⁰ cm⁴ sec/photon, as measuredby the above method); more preferably, greater than about twice that offluorescein (or, alternatively, greater than about 100×10⁻⁵⁰ cm⁴sec/photon); most preferably, greater than about three times that offluorescein (or, alternatively, greater than about 150×10⁻⁵⁰ cm⁴sec/photon); and optimally, greater than about four times that offluorescein (or, alternatively, greater than about 200×10⁻⁵⁰ cm⁴sec/photon).

Preferably, the photosensitizer is soluble in the reactive species (ifthe reactive species is liquid) or is compatible with the reactivespecies and with any binders (as described below) that are included inthe composition. Most preferably, the photosensitizer is also capable ofsensitizing 2-methyl-4,6-bis(trichloromethyl)-s-triazine undercontinuous irradiation in a wavelength range that overlaps the singlephoton absorption spectrum of the photosensitizer (single photonabsorption conditions), using the test procedure described in U.S. Pat.No. 3,729,313. Using currently available materials, that test can becarried out as follows:

A standard test solution can be prepared having the followingcomposition: 5.0 parts of a 5% (weight by volume) solution in methanolof 45,000-55,000 molecular weight, 9.0-13.0% hydroxyl content polyvinylbutyral (Butvar™ B76, Monsanto); 0.3 parts trimethylolpropanetrimethacrylate; and 0.03 parts2-methyl-4,6-bis(trichloromethyl)-s-triazine (see Bull. Chem. Soc.Japan, 42, 2924-2930 (1969)). To this solution can be added 0.01 partsof the compound to be tested as a photosensitizer. The resultingsolution can then be knife-coated onto a 0.05 mm clear polyester filmusing a knife orifice of 0.05 mm, and the coating can be air dried forabout 30 minutes. A 0.05 mm clear polyester cover film can be carefullyplaced over the dried but soft and tacky coating with minimum entrapmentof air. The resulting sandwich construction can then be exposed forthree minutes to 161,000 Lux of incident light from a tungsten lightsource providing light in both the visible and ultraviolet range (FCH™650 watt quartz-iodine lamp, General Electric). Exposure can be madethrough a stencil so as to provide exposed and unexposed areas in theconstruction. After exposure the cover film can be removed, and thecoating can be treated with a finely divided colored powder, such as acolor toner powder of the type conventionally used in xerography. If thetested compound is a photosensitizer, the trimethylolpropanetrimethacrylate monomer will be polymerized in the light-exposed areasby the light-generated free radicals from the2-methyl-4,6-bis(trichloromethyl)-s-triazine. Since the polymerizedareas will be essentially tack-free, the colored powder will selectivelyadhere essentially only to the tacky, unexposed areas of the coating,providing a visual image corresponding to that in the stencil.

Preferably, a photosensitizer can also be selected based in part uponshelf stability considerations. Accordingly, selection of a particularphotosensitizer can depend to some extent upon the particular reactivespecies utilized (as well as upon the choices of electron donor compoundand/or photoinitiator).

Particularly preferred multiphoton photosensitizers include thoseexhibiting large multiphoton absorption cross-sections, such asRhodamine B (that is,N-[9-(2-carboxyphenyl)-6-(diethylamino)-3H-xanthen-3-ylidene]-N-ethylethanaminiumchloride or hexafluoroantimonate) and the four classes ofphotosensitizers described, for example, by Marder and Perry et al. inInternational Patent Publication Nos. WO 98/21521 and WO 99/53242. Thefour classes can be described as follows: (a) molecules in which twodonors are connected to a conjugated π (pi)-electron bridge; (b)molecules in which two donors are connected to a conjugated π(pi)-electron bridge which is substituted with one or more electronaccepting groups; (c) molecules in which two acceptors are connected toa conjugated π (pi)-electron bridge; and (d) molecules in which twoacceptors are connected to a conjugated π (pi)-electron bridge which issubstituted with one or more electron donating groups (where “bridge”means a molecular fragment that connects two or more chemical groups,“donor” means an atom or group of atoms with a low ionization potentialthat can be bonded to a conjugated π (pi)-electron bridge, and“acceptor” means an atom or group of atoms with a high electron affinitythat can be bonded to a conjugated π (pi)-electron bridge).

Representative examples of such preferred photosensitizers include thefollowing:

The four above-described classes of photosensitizers can be prepared byreacting aldehydes with ylides under standard Wittig conditions or byusing the McMurray reaction, as detailed in International PatentPublication No. WO 98/21521.

Other compounds are described by Reinhardt et al. (for example, in U.S.Pat. Nos. 6,100,405, 5,859,251, and 5,770,737) as having largemultiphoton absorption cross-sections, although these cross-sectionswere determined by a method other than that described above.Representative examples of such compounds include:

(2) Electron Donor Compounds

Electron donor compounds useful in the multiphoton photoinitiator systemof the photoreactive compositions are those compounds (other than thephotosensitizer itself) that are capable of donating an electron to anelectronic excited state of the photosensitizer. Such compounds may beused, optionally, to increase the multiphoton photosensitivity of thephotoinitiator system, thereby reducing the exposure required to effectphotoreaction of the photoreactive composition. The electron donorcompounds preferably have an oxidation potential that is greater thanzero and less than or equal to that of p-dimethoxybenzene. Preferably,the oxidation potential is between about 0.3 and 1 volt vs. a standardsaturated calomel electrode (“S.C.E.”).

The electron donor compound is also preferably soluble in the reactivespecies and is selected based in part upon shelf stabilityconsiderations (as described above). Suitable donors are generallycapable of increasing the speed of cure or the image density of aphotoreactive composition upon exposure to light of the desiredwavelength.

When working with cationically-reactive species, those skilled in theart will recognize that the electron donor compound, if of significantbasicity, can adversely affect the cationic reaction. (See, for example,the discussion in U.S. Pat. No. 6,025,406 (Oxman et al.) at column 7,line 62, through column 8, line 49.)

In general, electron donor compounds suitable for use with particularphotosensitizers and photoinitiators can be selected by comparing theoxidation and reduction potentials of the three components (asdescribed, for example, in U.S. Pat. No. 4,859,572 (Farid et al.)). Suchpotentials can be measured experimentally (for example, by the methodsdescribed by R. J. Cox, Photograhpic Sensitivity, Chapter 15, AcademicPress (1973)) or can be obtained from references such as N. L. Weinburg,Ed., Technique of Electroorganic Synthesis Part II Techniques ofChemistry, Vol. V (1975), and C. K. Mann and K. K. Barnes,Electrochemical Reactions in Nonaqueous Systems (1970). The potentialsreflect relative energy relationships and can be used in the followingmanner to guide electron donor compound selection:

When the photosensitizer is in an electronic excited state, an electronin the highest occupied molecular orbital (HOMO) of the photosensitizerhas been lifted to a higher energy level (namely, the lowest unoccupiedmolecular orbital (LUMO) of the photosensitizer), and a vacancy is leftbehind in the molecular orbital it initially occupied. Thephotoinitiator can accept the electron from the higher energy orbital,and the electron donor compound can donate an electron to fill thevacancy in the originally occupied orbital, provided that certainrelative energy relationships are satisfied.

If the reduction potential of the photoinitiator is less negative (ormore positive) than that of the photosensitizer, an electron in thehigher energy orbital of the photosensitizer is readily transferred fromthe photosensitizer to the lowest unoccupied molecular orbital (LUMO) ofthe photoinitiator, since this represents an exothermic process. Even ifthe process is instead slightly endothermic (that is, even if thereduction potential of the photosensitizer is up to 0.1 volt morenegative than that of the photoinitiator) ambient thermal activation canreadily overcome such a small barrier.

In an analogous manner, if the oxidation potential of the electron donorcompound is less positive (or more negative) than that of thephotosensitizer, an electron moving from the HOMO of the electron donorcompound to the orbital vacancy in the photosensitizer is moving from ahigher to a lower potential, which again represents an exothermicprocess. Even if the process is slightly endothermic (that is, even ifthe oxidation potential of the photosensitizer is up to 0.1 volt morepositive than that of the electron donor compound), ambient thermalactivation can readily overcome such a small barrier.

Slightly endothermic reactions in which the reduction potential of thephotosensitizer is up to 0.1 volt more negative than that of thephotoinitiator, or the oxidation potential of the photosensitizer is upto 0.1 volt more positive than that of the electron donor compound,occur in every instance, regardless of whether the photoinitiator or theelectron donor compound first reacts with the photosensitizer in itsexcited state. When the photoinitiator or the electron donor compound isreacting with the photosensitizer in its excited state, it is preferredthat the reaction be exothermic or only slightly endothermic. When thephotoinitiator or the electron donor compound is reacting with thephotosensitizer ion radical, exothermic reactions are still preferred,but still more endothermic reactions can be expected in many instancesto occur. Thus, the reduction potential of the photosensitizer can be upto 0.2 volt (or more) more negative than that of a second-to-reactphotoinitiator, or the oxidation potential of the photosensitizer can beup to 0.2 volt (or more) more positive than that of a second-to-reactelectron donor compound.

Suitable electron donor compounds include, for example, those describedby D. F. Eaton in Advances in Photochemistry, edited by B. Voman et al.,Volume 13, pp. 427-488, John Wiley and Sons, New York (1986); by Oxmanet al. in U.S. Pat. No. 6,025,406 at column 7, lines 42-61; and byPalazzotto et al. in U.S. Pat. No. 5,545,676 at column 4, line 14through column 5, line 18. Such electron donor compounds include amines(including triethanolamine, hydrazine, 1,4-diazabicyclo[2.2.2]octane,triphenylamine (and its triphenylphosphine and triphenylarsine analogs),aminoaldehydes, and aminosilicones), amides (including phosphoramides),ethers (including thioethers), ureas (including thioureas), sulfinicacids and their salts, salts of ferrocyanide, ascorbic acid and itssalts, dithiocarbamic acid and its salts, salts of xanthates, salts ofethylene diamine tetraacetic acid, salts of (alkyl)_(n)(aryl)_(m)borates(n+m=4) (tetraalkylammonium salts preferred), various organometalliccompounds such as SnR₄ compounds (where each R is independently chosenfrom among alkyl, aralkyl (particularly, benzyl), aryl, and alkarylgroups) (for example, such compounds as n-C₃H₇Sn(CH₃)₃, (allyl)Sn(CH₃)₃,and (benzyl)Sn(n-C₃H₇)₃), ferrocene, and the like, and mixtures thereof.The electron donor compound can be unsubstituted or can be substitutedwith one or more non-interfering substituents. Particularly preferredelectron donor compounds contain an electron donor atom (such as anitrogen, oxygen, phosphorus, or sulfur atom) and an abstractablehydrogen atom bonded to a carbon or silicon atom alpha to the electrondonor atom.

Preferred amine electron donor compounds include alkyl-, aryl-, alkaryl-and aralkyl-amines (for example, methylamine, ethylamine, propylamine,butylamine, triethanolamine, amylamine, hexylamine, 2,4-dimethylaniline,2,3-dimethylaniline, o-, m- and p-toluidine, benzylamine, aminopyridine,N,N′-dimethylethylenediamine, N,N′-diethylethylenediamine,N,N′-dibenzylethylenediamine, N,N′-diethyl-1,3-propanediamine,N,N′-diethyl-2-butene-1,4-diamine, N,N′-dimethyl-1,6-hexanediamine,piperazine, 4,4′-trimethylenedipiperidine, 4,4′-ethylenedipiperidine,p-N,N-dimethyl-aminophenethanol and p-N-dimethylaminobenzonitrile);aminoaldehydes (for example, p-N,N-dimethylaminobenzaldehyde,p-N,N-diethylaminobenzaldehyde, 9-julolidine carboxaldehyde, and4-morpholinobenzaldehyde); and aminosilanes (for example,trimethylsilylmorpholine, trimethylsilylpiperidine,bis(dimethylamino)diphenylsilane, tris(dimethylamino)methylsilane,N,N-diethylaminotrimethylsilane, tris(dimethylamino)phenylsilane,tris(methylsilyl)amine, tris(dimethylsilyl)amine,bis(dimethylsilyl)amine, N,N-bis(dimethylsilyl)aniline,N-phenyl-N-dimethylsilylaniline, and N,N-dimethyl-N-dimethylsilylamine);and mixtures thereof. Tertiary aromatic alkylamines, particularly thosehaving at least one electron-withdrawing group on the aromatic ring,have been found to provide especially good shelf stability. Good shelfstability has also been obtained using amines that are solids at roomtemperature. Good photographic speed has been obtained using amines thatcontain one or more julolidinyl moieties.

Preferred amide electron donor compounds include N,N-dimethylacetamide,N,N-diethylacetamide, N-methyl-N-phenylacetamide,hexamethylphosphoramide, hexaethylphosphoramide,hexapropylphosphoramide, trimorpholinophosphine oxide,tripiperidinophosphine oxide, and mixtures thereof.

Preferred alkylarylborate salts include

-   Ar₃B⁻(n-C₄H₉)N⁺(C₂H₅)₄-   Ar₃B⁻(n-C₄H₉)N⁺(CH₃)₄-   Ar₃B⁻(n-C₄H₉)N⁺(n-C₄H₉)₄-   Ar₃B⁻(n-C₄H₉)Li⁺-   Ar₃B⁻(n-C₄H₉)N⁺(C₆H₁₃)₄-   Ar₃B⁻—(C₄H₉)N⁺(CH₃)₃(CH₂)₂OCO(CH₂)₂CH₃-   Ar₃B⁻—(C₄H₉)N⁺(CH₃)₃(CH₂)₂OCO(CH₂)₂CH₃-   Ar₃B⁻—(sec-C₄H₉)N⁺(CH₃)₃(CH₂)₂CO₂(CH₂)₂CH₃-   Ar₃B⁻—(sec-C₄H₉)N⁺(C₆H₁₃)₄-   Ar₃B⁻—(C₄H₉)N⁺(C₈H₁₇)₄-   Ar₃B⁻—(C₄H₉)N⁺(CH₃)₄-   (p-CH₃O—C₆H₄)₃B⁻(n-C₄H₉)N⁺(n-C₄H₉)₄-   Ar₃B⁻—(C₄H₉)N⁺(CH₃)₃(CH₂)₂OH-   ArB⁻(n-C₄H₉)₃N⁺(CH₃)₄-   ArB⁻(C₂H₅)₃N⁺(CH₃)₄-   Ar₂B⁻(n-C₄H₉)₂N⁺(CH₃)₄-   Ar₃B⁻(C₄H₉)N⁺(C₄H₉)₄-   Ar₄B⁻N⁺(C₄H₉)₄-   ArB⁻(CH₃)₃N⁺(CH₃)₄-   (n-C₄H₉)₄B⁻N⁺(CH₃)₄-   Ar₃B⁻(C₄H₉)P⁺(C₄H₉)₄    (where Ar is phenyl, naphthyl, substituted (preferably,    fluoro-substituted) phenyl, substituted naphthyl, and like groups    having greater numbers of fused aromatic rings), as well as    tetramethylammonium n-butyltriphenylborate and tetrabutylammonium    n-hexyl-tris(3-fluorophenyl)borate (available as CGI 437 and CGI 746    from Ciba Specialty Chemicals Corporation), and mixtures thereof.

Suitable ether electron donor compounds include 4,4′-dimethoxybiphenyl,1,2,4-trimethoxybenzene, 1,2,4,5-tetramethoxybenzene, and the like, andmixtures thereof. Suitable urea electron donor compounds includeN,N′-dimethylurea, N,N-dimethylurea, N,N′-diphenylurea,tetramethylthiourea, tetraethylthiourea, tetra-n-butylthiourea,N,N-di-n-butylthiourea, N,N′-di-n-butylthiourea, N,N-diphenylthiourea,N,N′-diphenyl-N,N′-diethylthiourea, and the like, and mixtures thereof.

Preferred electron donor compounds for free radical-induced reactionsinclude amines that contain one or more julolidinyl moieties,alkylarylborate salts, and salts of aromatic sulfinic acids. However,for such reactions, the electron donor compound can also be omitted, ifdesired (for example, to improve the shelf stability of thephotoreactive composition or to modify resolution, contrast, andreciprocity). Preferred electron donor compounds for acid-inducedreactions include 4-dimethylaminobenzoic acid, ethyl4-dimethylaminobenzoate, 3-dimethylaminobenzoic acid,4-dimethylaminobenzoin, 4-dimethylaminobenzaldehyde,4-dimethylaminobenzonitrile, 4-dimethylaminophenethyl alcohol, and1,2,4-trimethoxybenzene.

(3) Photoinitiators

Suitable photoinitiators (that is, electron acceptor compounds) for thereactive species of the photoreactive compositions are those that arecapable of being photosensitized by accepting an electron from anelectronic excited state of the multiphoton photosensitizer, resultingin the formation of at least one free radical and/or acid. Suchphotoinitiators include iodonium salts (for example, diaryliodoniumsalts), chloromethylated triazines (for example,2-methyl-4,6-bis(trichloromethyl)-s-triazine,2,4,6-tris(trichloromethyl)-s-triazine, and2-aryl-4,6-bis(trichloromethyl)-s-triazine), diazonium salts (forexample, phenyldiazonium salts optionally substituted with groups suchas alkyl, alkoxy, halo, or nitro), sulfonium salts (for example,triarylsulfonium salts optionally substituted with alkyl or alkoxygroups, and optionally having 2,2′ oxy groups bridging adjacent arylmoieties), azinium salts (for example, an N-alkoxypyridinium salt), andtriarylimidazolyl dimers (preferably, 2,4,5-triphenylimidazolyl dimerssuch as 2,2′,4,4′,5,5′-tetraphenyl-1,1′-biimidazole, optionallysubstituted with groups such as alkyl, alkoxy, or halo), and the like,and mixtures thereof.

The photoinitiator is preferably soluble in the reactive species and ispreferably shelf-stable (that is, does not spontaneously promotereaction of the reactive species when dissolved therein in the presenceof the photosensitizer and the electron donor compound). Accordingly,selection of a particular photoinitiator can depend to some extent uponthe particular reactive species, photosensitizer, and electron donorcompound chosen, as described above. If the reactive species is capableof undergoing an acid-initiated chemical reaction, then thephotoinitiator is an onium salt (for example, an iodonium, sulfonium, ordiazonium salt).

Suitable iodonium salts include those described by Palazzotto et al. inU.S. Pat. No. 5,545,676 at column 2, lines 28 through 46. Suitableiodonium salts are also described in U.S. Pat. Nos. 3,729,313,3,741,769, 3,808,006, 4,250,053 and 4,394,403. The iodonium salt can bea simple salt (for example, containing an anion such as Cl⁻, Br⁻, I⁻ orC₄H₅SO₃ ⁻) or a metal complex salt (for example, containing SbF₆ ⁻, PF₆⁻, BF₄ ⁻, tetrakis(perfluorophenyl)borate, SbF₅OH⁻ or AsF₆ ⁻). Mixturesof iodonium salts can be used if desired.

Examples of useful aromatic iodonium complex salt photoinitiatorsinclude diphenyliodonium tetrafluoroborate; di(4-methylphenyl)iodoniumtetrafluoroborate; phenyl-4-methylphenyliodonium tetrafluoroborate;di(4-heptylphenyl)iodonium tetrafluoroborate; di(3-nitrophenyl)iodoniumhexafluorophosphate; di(4-chlorophenyl)iodonium hexafluorophosphate;di(naphthyl)iodonium tetrafluoroborate;di(4-trifluoromethylphenyl)iodonium tetrafluoroborate; diphenyliodoniumhexafluorophosphate; di(4-methylphenyl)iodonium hexafluorophosphate;diphenyliodonium hexafluoroarsenate; di(4-phenoxyphenyl)iodoniumtetrafluoroborate; phenyl-2-thienyliodonium hexafluorophosphate;3,5-dimethylpyrazolyl-4-phenyliodonium hexafluorophosphate;diphenyliodonium hexafluoroantimonate; 2,2′-diphenyliodoniumtetrafluoroborate; di(2,4-dichlorophenyl)iodonium hexafluorophosphate;di(4-bromophenyl)iodonium hexafluorophosphate;di(4-methoxyphenyl)iodonium hexafluorophosphate;di(3-carboxyphenyl)iodonium hexafluorophosphate;di(3-methoxycarbonylphenyl)iodonium hexafluorophosphate;di(3-methoxysulfonylphenyl)iodonium hexafluorophosphate;di(4-acetamidophenyl)iodonium hexafluorophosphate;di(2-benzothienyl)iodonium hexafluorophosphate; and diphenyliodoniumhexafluoroantimonate; and the like; and mixtures thereof. Aromaticiodonium complex salts can be prepared by metathesis of correspondingaromatic iodonium simple salts (such as, for example, diphenyliodoniumbisulfate) in accordance with the teachings of Beringer et al., J. Am.Chem. Soc. 81, 342 (1959).

Preferred iodonium salts include diphenyliodonium salts (such asdiphenyliodonium chloride, diphenyliodonium hexafluorophosphate, anddiphenyliodonium tetrafluoroborate), diaryliodonium hexafluoroantimonate(for example, SarCat™ SR 1012 available from Sartomer Company), andmixtures thereof.

Useful chloromethylated triazines include those described in U.S. Pat.No. 3,779,778 (Smith et al.) at column 8, lines 45-50, which include2,4-bis(trichloromethyl)-6-methyl-s-triazine,2,4,6-tris(trichloromethyl)-s-triazine, and the more preferredchromophore-substituted vinylhalomethyl-s-triazines disclosed in U.S.Pat. Nos. 3,987,037 and 3,954,475 (Bonham et al.).

Useful diazonium salts include those described in U.S. Pat. No.4,394,433 (Gatzke), which comprise a light sensitive aromatic moiety(for example, pyrrolidine, morpholine, aniline, and diphenyl amine) withan external diazonium group (−N⁺=N) and an anion (for example, chloride,tri-isopropyl naphthalene sulfonate, tetrafluoroborate, and thebis(perfluoroalkylsulfonyl)methides) associated therewith. Examples ofuseful diazonium cations include 1-diazo-4-anilinobenzene,N-(4-diazo-2,4-dimethoxy phenyl)pyrrolidine,1-diazo-2,4-diethoxy-4-morpholino benzene, 1-diazo-4-benzoylamino-2,5-diethoxy benzene, 4-diazo-2,5-dibutoxy phenyl morpholino,4-diazo-1-dimethyl aniline, 1-diazo-N,N-dimethylaniline,1-diazo-4-N-methyl-N-hydroxyethyl aniline, and the like.

Useful sulfonium salts include those described in U.S. Pat. No.4,250,053 (Smith) at column 1, line 66, through column 4, line 2, whichcan be represented by the formulas:

wherein R₁, R₂, and R₃ are each independently selected from aromaticgroups having from about 4 to about 20 carbon atoms (for example,substituted or unsubstituted phenyl, naphthyl, thienyl, and furanyl,where substitution can be with such groups as alkoxy, alkylthio,arylthio, halogen, and so forth) and alkyl groups having from 1 to about20 carbon atoms. As used here, the term “alkyl” includes substitutedalkyl (for example, substituted with such groups as halogen, hydroxy,alkoxy, or aryl). At least one of R₁, R₂, and R₃ is aromatic, and,preferably, each is independently aromatic. Z is selected from the groupconsisting of a covalent bond, oxygen, sulfur, —S(=O)—, —C(═O)—,—(O═)S(═O)—, and —N(R)—, where R is aryl (of about 6 to about 20carbons, such as phenyl), acyl (of about 2 to about 20 carbons, such asacetyl, benzoyl, and so forth), a carbon-to-carbon bond, or—(R₄—)C(—R₅)—, where R₄ and R₅ are independently selected from the groupconsisting of hydrogen, alkyl groups having from 1 to about 4 carbonatoms, and alkenyl groups having from about 2 to about 4 carbon atoms.X⁻ is an anion, as described below.

Suitable anions, X⁻, for the sulfonium salts (and for any of the othertypes of photoinitiators) include a variety of anion types such as, forexample, imide, methide, boron-centered, phosphorous-centered,antimony-centered, arsenic-centered, and aluminum-centered anions.

Illustrative, but not limiting, examples of suitable imide and methideanions include (C₂F₅SO₂)₂N⁻, (C₄F₉SO₂)₂N⁻, (C₈F₁₇SO₂)₃C⁻, (CF₃SO₂)₃C⁻,(CF₃SO₂)₂N⁻, (C₄F₉SO₂)₃C⁻, (CF₃SO₂)₂(C₄F₉SO₂)C⁻(CF₃SO₂)(C₄F₉SO₂)N⁻,((CF₃)₂NC₂F₄SO₂)₂N⁻, (CF₃)₂NC₂F₄SO₂C⁻(SO₂ CF₃)₂,(3,5-bis(CF₃)C₆H₃)SO₂N⁻SO₂CF₃, C₆H₅SO₂C⁻(SO₂CF₃)₂, C₆H₅SO₂N⁻SO₂CF₃, andthe like. Preferred anions of this type include those represented by theformula (R_(f)SO₂)₃C⁻, wherein R_(f) is a perfluoroalkyl radical havingfrom 1 to about 4 carbon atoms.

Illustrative, but not limiting, examples of suitable boron-centeredanions include F₄B⁻, (3,5-bis(CF₃)C₆H₃)₄B⁻, (C₆F₅)₄B⁻, (p-CF₃C₆H₄)₄B⁻,(m-CF₃C₆H₄)₄B⁻, (p−-FC₆H₄)₄B⁻, (C₆F₅)₃(CH₃)B⁻, (C₆F₅)₃(n-C₄H₉)B⁻,(p-CH₃C₆H₄)₃(C₆F₅)B⁻, (C₆F₅)₃FB⁻, (C₆H₅)₃(C₆F₅)B⁻, (CH₃)₂(p-CF₃C₆H₄)₂B⁻,(C₆F₅)₃(n-C₁₈H₃₇O)B⁻, and the like. Preferred boron-centered anionsgenerally contain 3 or more halogen-substituted aromatic hydrocarbonradicals attached to boron, with fluorine being the most preferredhalogen. Illustrative, but not limiting, examples of the preferredanions include (3,5-bis(CF₃)C₆H₃)₄B⁻, (C₆F₅)₄B⁻, (C₆F₅)₃(n-C₄H₉)B⁻,(C₆F₅)₃FB⁻, and (C₆F₅)₃(CH₃)B⁻.

Suitable anions containing other metal or metalloid centers include, forexample, (3,5-bis(CF₃)C₆H₃)₄Al⁻, (C₆F₅)₄Al⁻, (C₆F₅)₂F₄P⁻, (C₆F₅)F₅P⁻,F₆P⁻, (C₆F₅)F₅Sb⁻, F₆Sb⁻, (HO)F₅Sb⁻, and F₆As⁻. The foregoing lists arenot intended to be exhaustive, as other useful boron-centerednonnucleophilic salts, as well as other useful anions containing othermetals or metalloids, will be readily apparent (from the foregoinggeneral formulas) to those skilled in the art.

Preferably, the anion, X⁻, is selected from tetrafluoroborate,hexafluorophosphate, hexafluoroarsenate, hexafluoroantimonate, andhydroxypentafluoroantimonate (for example, for use withcationically-reactive species such as epoxy resins).

Examples of suitable sulfonium salt photoinitiators include:

-   triphenylsulfonium tetrafluoroborate-   methyldiphenylsulfonium tetrafluoroborate-   dimethylphenylsulfonium hexafluorophosphate-   triphenylsulfonium hexafluorophosphate-   triphenylsulfonium hexafluoroantimonate-   diphenylnaphthylsulfonium hexafluoroarsenate-   tritolysulfonium hexafluorophosphate-   anisyldiphenylsulfonium hexafluoroantimonate-   4-butoxyphenyldiphenylsulfonium tetrafluoroborate-   4-chlorophenyldiphenylsulfonium hexafluorophosphate-   tri(4-phenoxyphenyl)sulfonium hexafluorophosphate-   di(4-ethoxyphenyl)methylsulfonium hexafluoroarsenate-   4-acetonylphenyldiphenylsulfonium tetrafluoroborate-   4-thiomethoxyphenyldiphenylsulfonium hexafluorophosphate-   di(methoxysulfonylphenyl)methylsulfonium hexafluoroantimonate-   di(nitrophenyl)phenylsulfonium hexafluoroantimonate-   di(carbomethoxyphenyl)methylsulfonium hexafluorophosphate-   4-acetamidophenyldiphenylsulfonium tetrafluoroborate-   dimethylnaphthylsulfonium hexafluorophosphate-   trifluoromethyldiphenylsulfonium tetrafluoroborate-   p-(phenylthiophenyl)diphenylsulfonium hexafluoroantimonate-   10-methylphenoxathiinium hexafluorophosphate-   5-methylthianthrenium hexafluorophosphate-   10-phenyl-9,9-dimethylthioxantheniun hexafluorophosphate-   10-phenyl-9-oxothioxanthenium tetrafluoroborate-   5-methyl-10-oxothianthrenium tetrafluoroborate-   5-methyl-10,10-dioxothianthrenium hexafluorophosphate

Preferred sulfonium salts include triaryl-substituted salts such astriarylsulfonium hexafluoroantimonate (for example, SarCat™ SR1010available from Sartomer Company), triarylsulfonium hexafluorophosphate(for example, SarCat™ SR 1011 available from Sartomer Company), andtriarylsulfonium hexafluorophosphate (for example, SarCat™ KI85available from Sartomer Company).

Useful azinium salts include those described in U.S. Pat. No. 4,859,572(Farid et al.) at column 8, line 51, through column 9, line 46, whichinclude an azinium moiety, such as a pyridinium, diazinium, ortriazinium moiety. The azinium moiety can include one or more aromaticrings, typically carbocyclic aromatic rings (for example, quinolinium,isoquinolinium, benzodiazinium, and naphthodiazonium moieties), fusedwith an azinium ring. A quaternizing substituent of a nitrogen atom inthe azinium ring can be released as a free radical upon electrontransfer from the electronic excited state of the photosensitizer to theazinium photoinitiator. In one preferred form, the quaternizingsubstituent is an oxy substituent. The oxy substituent, —O—T, whichquaternizes a ring nitrogen atom of the azinium moiety can be selectedfrom among a variety of synthetically convenient oxy substituents. Themoiety T can, for example, be an alkyl radical, such as methyl, ethyl,butyl, and so forth. The alkyl radical can be substituted. For example,aralkyl (for example, benzyl and phenethyl) and sulfoalkyl (for example,sulfomethyl) radicals can be useful. In another form, T can be an acylradical, such as an —OC(O)—T¹ radical, where T¹ can be any of thevarious alkyl and aralkyl radicals described above. In addition, T¹ canbe an aryl radical, such as phenyl or naphthyl. The aryl radical can inturn be substituted. For example, T¹ can be a tolyl or xylyl radical. Ttypically contains from 1 to about 18 carbon atoms, with alkyl moietiesin each instance above preferably being lower alkyl moieties and arylmoieties in each instance preferably containing about 6 to about 10carbon atoms. Highest activity levels have been realized when the oxysubstituent, —O—T, contains 1 or 2 carbon atoms. The azinium nuclei needinclude no substituent other than the quaternizing substituent. However,the presence of other substituents is not detrimental to the activity ofthese photoinitiators.

Useful triarylimidazolyl dimers include those described in U.S. Pat. No.4,963,471 (Trout et al.) at column 8, lines 18-28. These dimers include,for example,2-(o-chlorophenyl)-4,5-bis(m-methoxyphenyl)-1,1′-biimidazole;2,2′-bis(o-chlorophenyl)-4,4′,5,5′-tetraphenyl-1,1′-biimidazole; and2,5-bis(o-chlorophenyl)-4-[3,4-dimethoxyphenyl]-1,1′-biimidazole.

Preferred photoinitiators include iodonium salts (more preferably,aryliodonium salts), chloromethylated triazines, triarylimidazolyldimers (more preferably, 2,4,5-triphenylimidazolyl dimers), sulfoniumsalts, and diazonium salts. More preferred are aryliodonium salts,chloromethylated triazines, and the 2,4,5-triphenylimidazolyl dimers(with aryliodonium salts and the triazines being most preferred).

Preparation of Photoreactive Composition

The reactive species, multiphoton photosensitizers, electron donorcompounds, and photoinitiators can be prepared by the methods describedabove or by other methods known in the art, and many are commerciallyavailable. These four components can be combined under “safe light”conditions using any order and manner of combination (optionally, withstirring or agitation), although it is sometimes preferable (from ashelf life and thermal stability standpoint) to add the photoinitiatorlast (and after any heating step that is optionally used to facilitatedissolution of other components). Solvent can be used, if desired,provided that the solvent is chosen so as to not/react appreciably withthe components of the composition. Suitable solvents include, forexample, acetone, dichloromethane, and acetonitrile. The reactivespecies itself can also sometimes serve as a solvent for the othercomponents.

The three components of the photoinitiator system are present inphotochemically effective amounts (as defined above). Generally, thecomposition can contain at least about 5% (preferably, at least about10%; more preferably, at least about 20%) up to about 99.79%(preferably, up to about 95%; more preferably, up to about 80%) byweight of one or more reactive species; at least about 0.01%(preferably, at least about 0.1%; more preferably, at least about 0.2%)up to about 10% (preferably, up to about 5%; more preferably, up toabout 2%) by weight of one or more photosensitizers; optionally, up toabout 10% (preferably, up to about 5%) by weight of one or more electrondonor compounds (preferably, at least about 0.1%; more preferably, fromabout 0.1% to about 5%); and from about 0.1% to about 10% by weight ofone or more electron acceptor compounds (preferably, from about 0.1% toabout 5%) based upon the total weight of solids (that is, the totalweight of components other than solvent). When the reactive species is aleuco dye, the composition generally can contain from about 0.01% toabout 10% by weight of one or more reactive species (preferably, fromabout 0.3% to about 10%; more preferably, from about 1% to about 10%;most preferably, from about 2% to about 10%).

A wide variety of adjuvants can be included in the photoreactivecompositions, depending upon the desired end use. Suitable adjuvantsinclude solvents, diluents, resins, binders, plasticizers, pigments,dyes, inorganic or organic reinforcing or extending fillers (atpreferred amounts of about 10% to 90% by weight based on the totalweight of the composition), thixotropic agents, indicators, inhibitors,stabilizers, ultraviolet absorbers, medicaments (for example, leachablefluorides), and the like. The amounts and types of such adjuvants andtheir manner of addition to the compositions will be familiar to thoseskilled in the art.

It is within the scope of this invention to include nonreactivepolymeric binders in the compositions in order, for example, to controlviscosity and to provide film-forming properties. Such polymeric binderscan generally be chosen to be compatible with the reactive species. Forexample, polymeric binders that are soluble in the same solvent that isused for the reactive species, and that are free of functional groupsthat can adversely affect the course of reaction of the reactivespecies, can be utilized. Binders can be of a molecular weight suitableto achieve desired film-forming properties and solution rheology (forexample, molecular weights between about 5,000 and 1,000,000 daltons;preferably between about 10,000 and 500,000 daltons; more preferably,between about 15,000 and 250,000 daltons). Suitable polymeric bindersinclude, for example, polystyrene, poly(methyl methacrylate),poly(styrene)-co-(acrylonitrile), cellulose acetate butyrate, and thelike.

Prior to exposure, the resulting photoreactive compositions can becoated on a substrate, if desired, by any of a variety of coatingmethods known to those skilled in the art (including, for example, knifecoating and spin coating). The substrate can be chosen from a widevariety of films, sheets, and other surfaces, depending upon theparticular application and the method of exposure to be utilized.Preferred substrates are generally sufficiently flat to enable thepreparation of a layer of photoreactive composition having a uniformthickness. For applications where coating is less desirable, thephotoreactive compositions can alternatively be exposed in bulk form.

Exposure System and Its Use

Useful exposure systems include at least one light source (usually apulsed laser) and at least one optical element. Suitable light sourcesinclude, for example, femtosecond near-infrared titanium sapphireoscillators (for example, a Coherent Mira Optima 900-F) pumped by anargon ion laser (for example, a Coherent Innova). This laser, operatingat 76 MHz, has a pulse width of less than 200 femtoseconds, is tunablebetween 700 and 980 nm, and has average power up to 1.4 Watts. However,in practice, any light source that provides sufficient intensity (toeffect multiphoton absorption) at a wavelength appropriate for thephotosensitizer (used in the photoreactive composition) can be utilized.(Such wavelengths can generally be in the range of about 300 to about1500 nm; preferably, from about 600 to about 1100 nm; more preferably,from about 750 to about 850 nm. Peak intensities can generally rangefrom at least about 10⁶ W/cm². The upper limit of the pulse fluence isgenerally dictated by the ablation threshold of the photoreactivecomposition.) For example, Q-switched Nd:YAG lasers (for example, aSpectra-Physics Quanta-Ray PRO), visible wavelength dye lasers (forexample, a Spectra-Physics Sirah pumped by a Spectra-Physics Quanta-RayPRO), and Q-switched diode pumped lasers (for example, a Spectra-PhysicsFCbar™) can also be utilized. Preferred light sources are near infraredpulsed lasers having a pulse length less than about 10⁻⁸ second (morepreferably, less than about 10⁻⁹ second; most preferably, less thanabout 10⁻¹¹ second). Other pulse lengths can be used provided that theabove-detailed peak intensity and pulse fluence criteria are met.

Optical elements useful in carrying out the method of the inventioninclude refractive optical elements (for example, lenses and prisms),reflective optical elements (for example, retroreflectors or focusingmirrors), diffractive optical elements (for example, gratings, phasemasks, and holograms), polarizing optical elements (for example, linearpolarizers and waveplates), diffusers, Pockels cells, waveguides,waveplates, and birefringent liquid crystals, and the like. Such opticalelements are useful for focusing, beam delivery, beam/mode shaping,pulse shaping, and pulse timing. Generally, combinations of opticalelements can be utilized, and other appropriate combinations will berecognized by those skilled in the art. It is often desirable to useoptics with large numerical aperture to provide highly-focused light.However, any combination of optical elements that provides a desiredintensity profile (and spatial placement thereof) can be utilized. Forexample, the exposure system can include a scanning confocal microscope(BioRad MRC600) equipped with a 0.75 NA objective (Zeiss 20X Fluar).

Generally, exposure of the photoreactive composition can be carried outusing a light source (as described above) along with an optical systemas a means for controlling the three-dimensional spatial distribution oflight intensity within the composition. For example, the light from apulsed laser can be passed through a focusing lens in a manner such thatthe focal point is within the volume of the composition. The focal pointcan be scanned or translated in a three-dimensional pattern thatcorresponds to a desired shape, thereby creating a three-dimensionalimage of the desired shape. The exposed or illuminated volume of thecomposition can be scanned either by moving the composition itself or bymoving the light source (for example, moving a laser beam usinggalvo-mirrors).

If the light induces, for example, a reaction of the reactive speciesthat produces a material having solubility characteristics differentfrom those of the reactive species, the resulting image can optionallybe developed by removing either the exposed or the unexposed regionsthrough use of an appropriate solvent, for example, or by otherart-known means. Cured, complex, three-dimensional objects can beprepared in this manner.

Exposure times generally depend upon the type of exposure system used tocause image formation (and its accompanying variables such as numericalaperture, geometry of light intensity spatial distribution, the peaklight intensity during the laser pulse (higher intensity and shorterpulse duration roughly correspond to peak light intensity)), as well asupon the nature of the composition exposed (and its concentrations ofphotosensitizer, photoinitiator, and electron donor compound).Generally, higher peak light intensity in the regions of focus allowsshorter exposure times, everything else being equal. Linear imaging or“writing” speeds generally can be about 5 to 100,000 microns/secondusing a laser pulse duration of about 10⁻⁸ to 10⁻¹⁵ second (preferably,about 10⁻¹¹ to 10⁻¹⁴ second) and about 10² to 10⁹ pulses per second(preferably, about 10³ to 10⁸ pulses per second).

EXAMPLES

Objects and advantages of this invention are further illustrated by thefollowing examples, but the particular materials and amounts thereofrecited in these examples, as well as other conditions and details,should not be construed to unduly limit this invention.

Glossary

PSAN—poly(styrene-co-acrylonitrile) with weight average molecular weightof about 165,000, and 25 weight % acrylonitrile, available from Aldrich,Milwaukee, Wis.

SR-9008—alkoxylated trifunctional acrylate ester, available fromSartomer Co., Exton, Pa.

SR-368—tris(2-hydroxyethyl)isocyanurate triacrylate, available fromSartomer Co., Exton, Pa.

DPI PF₆—can be made essentially as described in column 4 of U.S. Pat.No. 4,394,403 (Smith), using silver hexafluorophosphate.

EDMAB—ethyl 4-dimethylaminobenzoate, available from Aldrich, Milwaukee,Wis.

TMSPMA—3-(trimethoxysilyl)propyl methacrylate, available from Aldrich,Milwaukee, Wis.

DIDMA —N-(2,6-diisopropyl)-N,N-dimethylaniline, available from Aldrich,Milwaukee, Wis.

CGI 7460—tetrabutylammonium n-hexyl-tris(3-fluorophenyl)borate,available from CIBA Specialty Chemicals Corp., Tarrytown, N.Y.

H—Nu 470—5,7-diiodo-3-butoxy-6-fluorone, available from Spectra Group,Ltd., Maumee, Ohio.

RhodamineB—N-[9-(2-carboxyphenyl)-6-(diethylamino)-3H-xanthen-3-ylidene]-N-ethylethanaminiumchloride, available from Aldrich, Milwaukee, Wis.

Epon™ SU-8 —bisphenol A novalac epoxy resin, also known as Epicote™ 157,available from Resolution Performance Products, Houston, Tex.

CD-1012—4-(2-hydroxytetradecanoxy)phenylphenyl iodoniumhexafluoroantimonate, available from Sartomer Co., Exton, Pa.

TMB—1,2,4-trimethoxybenzene, available from Aldrich, Milwaukee, Wis.

DPI SbF₆—can be made essentially as described in column 4 of U.S. Pat.No. 4,394,403 (Smith), using silver hexafluoroantimonate.

PMMA—120,000 molecular weight poly(methyl methacrylate), available fromAldrich, Milwauke, Wis.

Hydroxy Cyan LeucoDye—3′,5′di-tert-butyl-4′-hydroxybenzoyl-3,7-di(N,N-diethylamino)oxazine,which can be prepared as in Example 1 of U.S. Pat. No. 4,775,754 (Vogelet al).

CAB-551-1—cellulose acetate butyrate, available from Eastman Chemicals,Kingsport, Tenn.

Preparation of Multiphoton Photosensitizer I (MPS I)

Reaction of 1,4-bis(bromomethyl)-2,5-diethoxybenzene with triethylphosphate

1,4-Bis(bromomethyl)-2,5-dimethoxybenzene was prepared essentiallyaccording to the literature procedure (Syper et al, Tetrahedron, 39,781-792, 1983). The 1,4-bis(bromomethyl)-2,5-dimethoxybenzene (253 g,0.78 mol) was placed into a 1000 mL round bottom flask. Triethylphosphite (300 g, 2.10 mol) was added, and the reaction was heated tovigorous reflux with stirring for 48 hours under nitrogen atmosphere.The reaction mixture was cooled and the excess triethyl phosphite wasremoved under vacuum using a Kugelrohr apparatus. Upon heating to 100°C. at 0.1 mm Hg, a clear oil resulted. Upon cooling, the desired productsolidified and was suitable for use directly in the next step. The ¹HNMR spectrum of the product was consistent with the desired product.Recrystallization from toluene yielded colorless needles.

Synthesis of 1,4-bis-[4-(diphenylamino)styryl]-2,5-(dimethoxy)benzene(MPS I)

A 1000 mL round bottom flask was fitted with a calibrated droppingfunnel and a magnetic stirrer. The flask was charged with the productprepared from the above reaction (19.8 g, 45.2 mmol) andN,N-diphenylamino-p-benzaldehyde (25 g, 91.5 mmol available from FlukaChemical Corp., Milwaukee, Wis.). The flask was flushed with nitrogenand sealed with septa Anhydrous tetrahydrofuran (750 mL) was cannulatedinto the flask and all solids dissolved. The dropping funnel was chargedwith potassium tertiary butoxide (125 mL, 1.0 M in THF). The solution inthe flask was stirred, and the potassium tertiary butoxide solution wasadded to the contents of the flask over the course of 30 minutes. Thesolution was then left to stir at ambient temperature overnight. Thereaction was then quenched by the addition of water (500 mL). Stirringwas continued, and after about 30 minutes a highly fluorescent yellowsolid had formed in the flask. The solid was isolated by filtration,air-dried, and then recrystallized from toluene (450 mL). The desiredproduct (MPS I) was obtained as fluorescent needles (24.7 g, 81% yield).The ¹H NMR spectrum of the product was consistent with the proposedstructure.

Examples 1-2

A stock solution was prepared by adding 30 g PSAN to 120 g dioxane, andmixing overnight on a roller. A second solution was prepared by adding 1g of MPS I to 35 g SR-9008, then heating and stirring to partiallydissolve the photosensitizer. The second solution was added to the stocksolution and allowed to mix overnight on a roller. To this solution wasadded 35 g SR-368 and the solution allowed to mix overnight on a roller,providing masterbatch A. In two separate vials, 11 g of masterbatch Awas placed. 0.1 g DPI PF6 was dissolved in 1 ml of acetonitrile andadded to the first vial containing 11 g of masterbatch A and theresulting solution mixed by agitation and then used in Example 1. 0.1 gDPI PF6 and 0.1 g EDMAB were dissolved in 1 ml of acetonitrile and addedto the second vial containing 11 g masterbatch A, and the resultingsolution used in Example 2.

Two milliliters of each of the two solutions prepared above werefiltered through a 0.45 μm syringe filter and coated with a spin coateronto silicon wafers (that had been previously treated with TMSPMA) at3000 RPM for 40 sec, and baked at 80° C. for 40 min to remove solvent.

The resulting coated films were patterned by focusing the output of aSpectra-Physics Ti-sapphire laser (100 fs pulses, 80 MHz, 800 nm) (laseravailable from Spectra-Physics, Mountain View. Calif. as part of“Hurricane” system), using a 10×, 0.25 NA (numeric aperture) microscopeobjective, into the film and moving the film mounted on a computercontrolled, motorized X-Y stage (NEAT LM-600 stage, available from NewEngland Affiliated Technologies, Lawrence, Mass.). Based on gaussianoptics formulae, the diameter of the focussed spot was approximately 8μm. The average laser power was measured using an Ophir calibratedphotodiode (available from Ophir Optronics Inc., Danvers, Mass.). Toassess the photosensitivity of different formulations, a pattern oflines was produced where for each line the speed of the stage wasincreased by a factor of √{square root over (2)} to cover a range from77 to 27520 μm/sec. Following imaging, the patterns were developed bydipping in dimethylformamide for one minute, rinsing in isopropylalcohol and air drying.

Table 1 summarizes the threshold writing speed for Examples 1 and 2.Threshold writing speed corresponded to the last line visible in thepattern when examined using an optical microscope.

TABLE 1 Threshold Writing Speed of Two- and Three-ComponentPhotoinitiator Systems in Acrylate Resin. Photoinitiator ThresholdThreshold System Writing Writing Example Photopolymer (% by weight SpeedSpeed Number Formulation of resin solids) (17 mW) (33 mW) 1 PSAN, SR-MPS I (1%), 1742 3440 9008, SR-368 DPI PF6 (2%) μm/sec μm/sec 2 PSAN,SR9008, MPS I (1%), 1742 4960 SR368 DPI PF6 (2%), μm/sec μm/sec EDMAB(2%)The results in Table 1 show high writing speeds, and a particularly highwriting speed at the higher laser intensity when the electron donorcompound, EDMAB, was used with the photosensitizer and photoinitiator.

Examples 3-6 and Comparative Example C1

A stock solution was prepared by adding 30 g PMMA to 120 g dioxane, andmixing overnight on a roller. A second solution was prepared by adding 1g of MPS I to 35 g Sartomer™ SR9008, then heating and stirring topartially dissolve the photosensitizer. The second solution was added tothe stock solution and allowed to mix overnight on a roller. To thissolution was added 35 g Sartomer™ SR368 and the solution allowed to mixovernight on a roller, providing masterbatch B. In five separate vials,11 g of masterbatch B was placed. 1 ml acetonitrile was added to thefirst vial containing 11 g of masterbatch B and the solution mixed byagitation (Comparative Example C1). 0.1 g DPI PF6 was dissolved in 1mlof acetonitrile and added to the second vial containing 11 g ofmasterbatch B and the solution mixed by agitation (Example 3). 0.1 g DPIPF6 and 0.1 g EDMAB was dissolved in acetonitrile and added to the thirdvial containing 11 g masterbatch B and the solution mixed by agitation(Example 4). 0.1 g DPI PF6 and 0.1 g DIDMA was dissolved in acetonitrileand added to the third vial containing 11 g masterbatch B and thesolution mixed by agitation (Example 5). 0.1 g DPI PF6 and 0.1 g CGI7460 (alkyltriarylborate salt) was dissolved in 1 ml of acetonitrile andadded to the fourth vial containing 11 g of masterbatch B and thesolution mixed by agitation (Example 6).

Two milliliters of each of the five solutions prepared above werefiltered through a 0.45 μm syringe filter and coated with a spin coateronto silicon wafers (that had been previously treated with TMSPMA) at3000 RPM for 40 sec, and baked at 80° C. for 40 min to remove solvent.

The coated films were patterned essentially as in Example 1 by focusingthe output of a Spectra-Physics Ti-sapphire laser (100 fs pulses, 80MHz, 800 nm) using a 10×, 0.25 NA microscope objective into the film andmoving the film mounted on a NEAT LM-600 computer controlled, motorizedX-Y stage. Based on gaussian optics formulae, the diameter of thefocussed spot is approximately 8 um. The average laser power wasmeasured as the beam exited the objective using an Ophir calibratedphotodiode. To assess the photosensitivity of different formulations, apattern of lines was produced where for each line, the speed of thestage was increased by a factor of √{square root over (2)} to cover arange from 77 to 27520 μm/s. Following imaging, the patterns weredeveloped by dipping the patterned films in dimethylformamide for oneminute, rinsing in isopropyl alcohol, and air dry. The threshold writingspeed was defined as the last line visible in the pattern when examinedusing an optical microscope.

Table 2 summarizes the threshold writing speeds for Examples 3-6 andComparative Example C1 with two different laser intensities. Thethreshold writing speed when photosensitizer was used alone was 430 μm/swith 75 mW average laser power.

TABLE 2 Threshold Writing Speed of One-, Two- and Three-ComponentSystems in Acrylate Resin. Photoinitiator Threshold Threshold Photo-System (% Writing Writing Example polymer by weight of Speed SpeedNumber Formulation resin solids) (17 mW) (33 mW) C1 PMMA, MPS I (1%)<<77 μm/s 55 μm/s SR9008, SR368 3 PMMA, MPS I (1%), 1480 μm/s 4960 μm/sSR9008, DPI PF6 (2%) SR368 4 PMMA, MPS I (1%), 1720 μm/s 4960 μm/sSR9008, DPI PF6 (2%), SR368 EDMAB (2%) 5 PMMA, MPS I (1%), 1720 μm/s3440 μm/s SR9008, DPI PF6 (2%), SR368 DIDMA (2%) 6 PMMA, MPS I (1%),3440 μm/s 13760 μm/s SR9008, DPI PF6 (2%), SR368 CGI 7460 (2%)The results in Table 2 show that high writing speeds were achieved whenthe two- and three-component photoinitiator systems were used, and aparticularly high writing speed was achieved at the higher laserintensity when the electron donor compound, EDMAB, was used with thephotosensitizer and photoinitiator.

Example 7

Coated films were prepared and patterned essentially as in Example 6 at4, 6, 11, 17 and 30 mW average laser power, and threshold writing speedswere determined essentially as in Examples 3-6. The threshold writingspeed scaled quadratically with the average power, as shown in FIG. 1,consistent with a two-photon induced photopolymerization.

Comparative Examples C9-C12

(Use of Fluorone Photosensitizer)

A stock solution was prepared by adding 30 g PMMA to 120 g dioxane, andmixing overnight on a roller. A second solution was prepared by adding 1g of H—Nu 470 (photosensitizer) to 35 g Sartomer™ SR9008, then heatingand stirring to partially dissolve the photosensitizer. The secondsolution was added to the stock solution and allowed to mix overnight ona roller. To the resulting solution was added 35 g Sartomer™ SR368, andthe solution was allowed to mix overnight on a roller, providingmasterbatch B. Masterbatch B (1 g) was mixed with 10 g of the abovestock solution, and 0.025 g DPI PF6 and 0.025 g DIDMA were added andmixed with agitation (Comparative Example C2). In three separate vials,11 g of masterbatch B was placed. 0.1 g DIDMA was dissolved in 1 ml ofacetonitrile and added to the first vial containing 11 g of masterbatchB with mixing by agitation (Comparative Example C3). 0.1 g DPI PF6 wasdissolved in 1 ml acetonitrile and added to the second vial containing11 g masterbatch B with mixing by agitation (Comparative Example C4).0.1 g DPI PF6 and 0.1 DIDMA were dissolved in 1 ml of acetonitrile andadded to the third vial containing 11 g of masterbatch B with mixing byagitation (Comparative Example C5).

Two milliliters of each of the four resulting solutions prepared abovewere filtered through a 0.45 μm syringe filter and coated with a spincoater onto silicon wafers (that had been previously treated withTMSPMA) at 3000 RPM for 40 sec, and baked at 80° C. for 40 min to removesolvent.

The coated films were patterned essentially as in Example 1 by focusingthe output of a Spectra-Physics Ti-sapphire laser (100 fs pulses, 80MHz, 800 nm), using a 10×, 0.25 NA microscope objective, into the filmand moving the film mounted on a on a NEAT LM-600 computer controlled,motorized X-Y stage. Based on gaussian optics formulae, the diameter ofthe focussed spot was approximately 8 um. The average laser power wasmeasured as the beam exited the objective using an Ophir calibratedphotodiode. To assess the photosensitivity of different formulations, apattern of lines was produced where for each line, the speed of thestage was increased by a factor of √{square root over (2)} to cover arange from 77 to 27520 μm/s. Following imaging, the patterns weredeveloped by dipping the patterned films in dimethylformamide for oneminute, rinsing in isopropyl alcohol, and air drying. The thresholdwriting speed was defined as the last line visible in the pattern whenexamined using an optical microscope.

Table 3 summarizes the threshold writing speeds for Comparative ExamplesC2-C5 with two different laser intensities.

TABLE 3 Threshold Writing Speeds for Compositions Comprising FluoronePhotosensitizer. Photo- initiator System Threshold Threshold ComparativePhoto- (% by Writing Writing Example polymer weight of Speed SpeedNumber Formulation resin solids) (250 mW) (331 mW) C2 PMMA, H-Nu 470 0μm/s 0 μm/s SR9008, (0.18%), SR368 DIDMA (1%), DPI PF6 (1%) C3 PMMA,H-Nu 470 0 μm/s 215 μm/s SR9008, (1%), SR368 DIDMA (2%) C4 PMMA, H-Nu470 0 μm/s 77 μm/s SR9008, (1%), DPI SR368 PF6 (2%) C5 PMMA, H-Nu 4701240 μm/s 3440 μm/s SR9008, (1%), SR368 DIDMA (2%), DPI PF6 (2%)The results in Table 3 show that when H-Hu 470 was used as thephotosensitizer with electron donor compound and/or photoinitiator anorder of magnitude higher laser power was required than that requiredfor compositions using photosensitizers with large two-photon absorptioncross-sections (Examples 1-7).

Examples 8-11

(Cationic Polymerization of Epoxy)

Rhodamine B (4.2 g) was dissolved in 220 ml water and filtered throughinfusorial earth. To the filtrate was added, with stirring, 10.0 gsodium hexafluoroantimonate, and the mixture was allowed to stir forabout 5 minutes. The resulting mixture with a precipitate was filteredthrough a frit, and the solid was washed with water and dried overnightin an oven at 80° C., to yield 4.22 g rhodamine B hexafluoroantimonatesalt (Rh B SBF6). The structure was confirmed by proton and fluorineNMR.

Epon™ SU-8 (60 g), was mixed with 60 g methylisobutyl ketone, warmed to50-75° C., and agitated with magnetic stirring until dissolve, resultingin a stock solution. To 25 g of stock solution was added 0.0625 g Rh BSbF6 predissolved in 0.2 ml acetonitrile with mixing by agitation toform masterbatch D. To each of 4 vials was added 5 g masterbatch D. Tothe first vial was added 0.025 g SR-1012 with mixing by agitation(Example 8). To the second vial was added 0.025 SR-1012 and 0.0275 g TMBwith mixing by agitation (Example 9). To the third vial was added 0.025g DPI SbF6 with mixing by agitation (Example 10). To the fourth vial wasadded 0.025 g DPI SbF6 and 0.0125 g EDMAB with mixing by agitation(Example 11).

Two milliliters of each of the four resulting solutions prepared abovewere filtered through a 0.45 μm syringe filter and coated with a spincoater onto silicon wafers (that had been previously treated withTMSPMA) at 3000 RPM for 40 sec, and baked at 80° C. for 40 min to removesolvent.

The coated films were patterned essentially as in Example 1 by afocusing the output of a Spectra-Physics Ti-sapphire laser (100 fspulses, 80 MHz, 800 nm), using a 10×, 0.25 NA microscope objective, intothe film and moving the film mounted on a NEAT LM-600 computercontrolled, motorized X-Y stage. Based on gaussian optics formulae, thediameter of the focussed spot is approximately 8 um. The average laserpower was measured as the beam exited the objective using an Ophircalibrated photodiode. To assess the photosensitivity of differentformulations, a pattern of lines was produced where for each line, thespeed of the stage was increased by a factor of √{square root over (2)}to cover a range from 77 to 27520 um/s. Following patterning, eachsample was subjected to a post-exposure bake at 130° C. for 5 minutes ona hotplate, and the patterns were developed by dipping the patternedfilms in dimethylformamide for one minute, rinsing in isopropyl alcohol,and air drying. The threshold writing speed was defined as the last linevisible in the pattern when examined using an optical microscope.

Table 4 summarizes the threshold writing speeds for Examples 8-11 withthree different laser intensities.

TABLE 4 Threshold Writing Speeds for Cationic Polymerization of EpoxyResin Containing Photosensitizer, Electron Donor Compound and/orPhotoinitiator. Photo- initiator Threshold Threshold Photo- SystemWriting Writing Example polymer (% by weight Speed Speed NumberFormulation of resin solids) (144 mW) (337 mW) 8 SU-8 RhB SbF6 155 μm/sNR (0.5%), SR- 1012 (1%) 9 SU-8 RhB SbF6 155 μm/s NR (0.5%), SR- 1012(1%), TMB (1.1%) 10 SU-8 RhB SbF6 NR 6880 μm/s (0.5%), DPI SbF6 (1%) 11SU-8 RhB SbF6 NR 1720 μm/s (0.5%), DPI SbF6 (1%), EDMAB (0.5%) NR = notrun.The results in Table 4 show that cationic polymerization occurred in thepresence of electron donor compound.

Example 12

Four solutions were made up with the following amounts and compoundsunder “Safe lights”, excluding any ambient light from the solutions.

Solution A

-   Hydroxy Cyan Leuco Dye, 3 mg-   SR-1012, 3 mg-   dichloromethane, 3 g    Solution B-   Hydroxy Cyan Leuco Dye, 5.5 mg-   MPS I, 5.5 mg-   dichloromethane, 5.5 g    Solution C-   SR-1012, 5 mg-   MPS I, 5 mg-   dichloromethane, 5 g    Solution D-   Hydroxy Cyan Leuco Dye, 5 mg-   SR-1012, 5 mg-   MPS I, 5 mg-   dichloromethane, 5 g.

Each solution A-D was spotted onto a piece of hardened filter paper. Thesolvent was allowed to evaporate. Each spot on the filter paper was thenirradiated by focusing the output of a Spectra-Physics Ti-sapphire laser(100 fs pulses, 80 MHz, 800 nm), using a 10×, 0.25 NA microscopeobjective, into the spot on the filter paper and moving the filter papermounted on a NEAT LM-600 computer controlled, motorized X-Y stage insuch a way as to expose a square 1 mm by 1 mm in the center of eachspot. A laser power of 75 mW was used. Only the spot from solution Ddeveloped, resulting in a color change from slight yellow to blue in the1 mm by 1 mm area exposed to the laser. Thus, the leuco dye wasdeveloped through multiphoton absorption using the photoinitiator systemmade up of the photosensitizer and photoinitiator.

Example 13

A small vial was charged with the following: Hydroxy Cyan Leuco Dye (25mg), SR-1012 (25 mg), MPS I (25 mg), and dichloromethane (4 g). To thisvial was added 4 g of CAB-551-1 (20% solids in dichloropropane) withmixing and exclusion of light. The resulting solution was then spincoated onto a glass slide. After evaporation of the dichloropropane, anarea of the resulting coating approximately 2 mm square was exposedessentially as in Example 12. This area, and this area only, developedby a color change from yellow to blue-green.

Example 14

A coating solution is prepared by dissolving in an appropriate solvent(such as MEK) acrylate-based monomers and oligomers (such astrimethylolpropane triacrylate, SR454™, available from Sartomer Co.,Inc., Exton, Pa.) and binder (such as poly(methyl methacrylate),available from Aldrich Chemical Co., Milwaukee, Wis.) in a ratio of60:27.5:12.5. To this solution is added a photoinitiator system,including a multiphoton photosensitizer with large cross-section formultiphoton absorption (such as bis(diphenylamino)stilbene, availablefrom Aldrich Chemical Co.), an 'onium salt (such as diphenyliodoniumhexafluorophosphate, described in U.S. Pat. No. 5,545,676, Example 1)and an electron donor such as ethyl dimethylaminobenzoate (availablefrom Aldrich Chemical Co.). The amounts of the components of thephotoinitiator system are chosen such that the concentrations of eachcomponent as a percentage of solids is about 0.5% multiphotonphotosensitizer, 1% 'onium salt, and 1% electron donor. The solution iscoated (knife coated, for example) on a substrate (such as a siliconwafer) and the solvent evaporated to yield a coating with dry thicknessof about 0.125 mm. Exposure using a focussed, pulsed laser of about 700nm (such as a Ti-Sapphire laser) in a pattern causes polymerization andinsolubilization of the coating, revealed by rinsing the coating with asolvent (such as MEK) and removing the unexposed coating.

Example 15

A coating solution is prepared by dissolving in an appropriate solvent(such as MEK) an epoxy-functional monomer (such as ERL 4221™, acycloaliphatic epoxy compound available from union Carbide Co., Danbury,Conn.) and binder (such as poly(methyl methacrylate)) in a ratio of60:27.5:12.5. To this solution is added a photoinitiator system,including a multiphoton photosensitizer with large cross-section formultiphoton absorption (such as bis(diphenylamino)stilbene), an 'oniumsalt such as diphenyliodonium hexafluoroantimonate, and an electrondonor such as ethyl dimethylaminobenzoate. The amounts of the componentsof the photoinitiator system are chosen such that the concentrations ofeach component as a percentage of solids is about 0.5% multiphotonphotosensitizer, 1% 'onium salt, and 0.5% electron donor. The solutionis coated (knife coated, for example) on a substrate (such as a siliconwafer) and the solvent evaporated to yield a coating with dry thicknessof about 0.125 mm. Exposure using a focussed, pulsed laser of about 700nm (such as a Ti-Sapphire laser) in a pattern causes polymerization andinsolubilization of the coating, revealed by rinsing the coating with asolvent (such as MEK) and removing the unexposed coating.

Example 16

MPS I (16.7 mg) and DPI PF₆ (60 mg) were dissolved in 1 ml dioxane. Theresulting solution was then added to 24.0 g of tetrahydropyranylmethacrylate (THP-MA) solution (14% solid in 1-methoxy-2-propanol) toform a two-component solution . A film (˜100 μm thick) of thetwo-component solution was cast on a glass slide and baked at 90° C. for15 minutes on a hot plate. The resulting sample was placed horizontallyon a movable stage. A Ti:Sapphire laser (part of a Hurricane™ systemmanufactured by Spectra-Physics, Inc.; 800 nm, 100 fs pulses, 80 mHz)was used for exposure of the film. The power used was 17 mW, and theobjective lens used was a 10× (N.A. 0.25). The laser beam was focusedtoward the film-glass slide interface. The stage moved over a range ofspeeds (started with 28 and ended with 5120 μm/sec) as the film wasexposed. After a post-exposure bake (PEB) at 90° C. for 5 minutes on ahot plate, the film was developed with 2% Na₂CO₃ solution for 5 minutes.Lines with writing speed of 28, 40, 56, and 80 μm/sec were observed.

Example 17

5.0 mg of trimethoxybenzene is added to 10 g of the two-componentsolution of Example 16 to provide a three-component solution. A film ofthe three-component solution is cast, baked, and exposed in the samemanner as in Example 16. After development in 2% Na₂CO₃ solution for 5minutes, lines with writing speeds of 28, 40, 56, and 80 μm/sec areobserved.

The complete disclosures of the patents, patent documents, andpublications cited herein are incorporated by reference in theirentirety as if each were individually incorporated. Variousmodifications and alterations to this invention will become apparent tothose skilled in the art without departing from the scope and spirit ofthis invention. It should be understood that this invention is notintended to be unduly limited by the illustrative embodiments andexamples set forth herein and that such examples and embodiments arepresented by way of example only with the scope of the inventionintended to be limited only by the claims set forth herein as follows.

1. A method of multiphoton photosensitizing comprising (a) preparing aphotoreactive composition comprising (1) at least one reactive speciesthat is capable of undergoing an acid- or radical-initiated chemicalreaction; and (2) at least one multiphoton photoinitiator systemcomprising photochemically effective amounts of (i) at least onemultiphoton photosensitizer that is capable of simultaneously absorbingat least two photons and that has a two-photon absorption cross-sectiongreater than that of fluorescein; (ii) optionally, at least one electrondonor compound different from said multiphoton photosensitizer andcapable of donating an electron to an electronic excited state of saidphotosensitizer; and (iii) at least one photoinitiator that is capableof being photosensitized by accepting an electron from an electronicexcited state of said photosensitizer, resulting in the formation of atleast one free radical and/or acid; and (b) irradiating said compositionwith light sufficient to cause simultaneous absorption of at least twophotons, thereby inducing at least one acid- or radical-initiatedchemical reaction where said composition is exposed to the light; withthe proviso that said multiphoton photoinitiator system comprises atleast one electron donor compound whenever said photoreactivecomposition comprises at least one said reactive species that is capableof undergoing an acid-initiated chemical reaction and that is either acurable species or a non-curable, reactive polymer.
 2. The method ofclaim 1 wherein said reactive species is a curable species.
 3. Themethod of claim 2 wherein said curable species is selected from thegroup consisting of monomers, oligomers, reactive polymers, and mixturesthereof.
 4. The method of claim 3 wherein said curable species isselected from the group consisting of addition-polymerizable monomersand oligomers, addition-crosslinkable polymers,cationically-polymerizable monomers and oligomers,cationically-crosslinkable polymers, and mixtures thereof.
 5. The methodof claim 1 wherein said reactive species is a non-curable species. 6.The method of claim 1 wherein said multiphoton photosensitizer has atwo-photon absorption cross-section greater than about 50×10⁻⁵⁰ cm⁴sec/photon.
 7. The method of claim 1 wherein said multiphotonphotosensitizer has a two-photon absorption cross-section greater thanabout 1.5 times that of fluorescein.
 8. The method of claim 1 whereinsaid multiphoton photosensitizer has a two-photon absorptioncross-section greater than about 75×10⁻⁵⁰ cm⁴ sec/photon.
 9. The methodof claim 1 wherein said multiphoton photosensitizer has a two-photonabsorption cross-section greater than about 2 times that of fluorescein.10. The method of claim 1 wherein said multiphoton photosensitizer has atwo-photon absorption cross-section greater than about 100×10⁻⁵⁰ cm⁴sec/photon.
 11. The method of claim 1 wherein said multiphotonphotosensitizer has a two-photon absorption cross-section greater thanabout 3 times that of fluorescein.
 12. The method of claim 1 whereinsaid multiphoton photosensitizer has a two-photon absorptioncross-section greater than about 150×10⁻⁵⁰ cm⁴ sec/photon.
 13. Themethod of claim 1 wherein said multiphoton photosensitizer has atwo-photon absorption cross-section greater than about 4 times that offluorescein.
 14. The method of claim 1 wherein said multiphotonphotosensitizer has a two-photon absorption cross-section greater thanabout 200×10⁻⁵⁰ cm⁴ sec/photon.
 15. The method of claim 1 wherein saidmultiphoton photosensitizer is Rhodamine B.
 16. The method of claim 1wherein said multiphoton photosensitizer is selected from the followingcompounds:


17. The method of claim 1 wherein said electron donor compound has anoxidation potential that is greater than zero and less than or equal tothat of p-dimethoxybenzene.
 18. The method of claim 1 wherein saidelectron donor compound has an oxidation potential between about 0.3 and1 volt vs. a standard saturated calomel electrode.
 19. The method ofclaim 1 wherein said electron donor compound is selected from the groupconsisting of amines, amides, ethers, ureas, sulfinic acids and theirsalts, salts of ferrocyanide, ascorbic acid and its salts,dithiocarbamic acid and its salts, salts of xanthates, salts of ethylenediamine tetraacetic acid, salts of (alkyl)_(n)(aryl)_(m)borates (n+m=4), SnR₄ compounds (where each R is independently chosen from the groupconsisting of alkyl, aralkyl, aryl, and alkaryl groups), ferrocene, andmixtures thereof.
 20. The method of claim 19 wherein said electron donorcompound is selected from the group consisting of amines that containone or more julolidinyl moieties, alkylarylborate salts, salts ofaromatic sulfinic acids, 4-dimethylaminobenzoic acid, ethyl4dimethylaminobenzoate, 3-dimethylaminobenzoic acid,4-dimethylaminobenzoin, 4-dimethylaminobenzaldehyde,4-dimethylaminobenzonitrile, 4-dimethylaminophenethyl alcohol,1,2,4-trimethoxybenzene, and mixtures thereof.
 21. The method of claim 1wherein said photoreactive composition contains no electron donorcompound.
 22. The method of claim 1 wherein said photoinitiator isselected from the group consisting of iodonium salts, sulfonium salts,diazonium salts, azinium salts, chloromethylated triazines,triarylimidazolyl dimers, and mixtures thereof.
 23. The method of claim22 wherein said photoinitiator is selected from the group consisting ofiodonium salts, chloromethylated triazines, triarylimidazolyl dimers,sulfonium salts, diazonium salts, and mixtures thereof.
 24. The methodof claim 23 wherein said photoinitiator is selected from the groupconsisting of aryliodonium salts, chloromethylated triazines,2,4,5-triphenylimidazolyl dimers, and mixtures thereof.
 25. The methodof claim 1 wherein said photoreactive composition comprises from about5% to about 99.79% by weight of said at least one reactive species, fromabout 0.01% to about 10% by weight of said at least one multiphotonphotosensitizer, up to about 10% by weight of said at least one electrondonor compound, and from about 0.1% to about 10% by weight of said atleast one photoinitiator, based upon the total weight of solids.
 26. Themethod of claim 1 wherein said photoreactive composition furthercomprises at least one adjuvant selected from the group consisting ofsolvents, diluents, resins, binders, plasticizers, pigments, dyes,inorganic or organic reinforcing or extending fillers, thixotropicagents, indicators, inhibitors, stabilizers, ultraviolet absorbers, andmedicaments.
 27. The method of claim 1 wherein said irradiating is pulseirradiating.
 28. The method of claim 27 wherein said pulse irradiatingis carried out using a near infrared pulsed laser having a pulse lengthless than about 10⁻⁸ second.
 29. The method of claim 1 wherein saidmethod provides linear imaging speeds of about 5 to about 100,000microns/second using a laser pulse duration of about 10⁻⁸ to 10⁻¹⁵second and about 10² to 10⁹ pulses per second.
 30. A method ofmultiphoton photosensitizing comprising (a) preparing a photoreactivecomposition comprising (1) at least one curable species that is capableof undergoing a radical-initiated chemical reaction; and (2) at leastone multiphoton photoinitiator system comprising photochemicallyeffective amounts of (i) Rhodamine B; (ii) optionally, at least onealkylarylborate salt; and (iii) at least one iodonium salt; and (b)irradiating said composition with light sufficient to cause simultaneousabsorption of at least two photons, thereby inducing at least oneradical-initiated chemical reaction where said composition is exposed tothe light.
 31. A method of multiphoton photosensitizing, the methodcomprising pulse irradiating a multiphoton-curable composition withlight sufficient to cause simultaneous absorption of at least twophotons, thereby curing the multiphoton-curable composition whereexposed to the light, wherein the multiphoton-curable compositioncomprises: at least one curable species selected from the groupconsisting of monomers, oligomers, and reactive polymers; a multiphotonphotoinitiator system comprising photochemically effective amounts of:at least one multiphoton photosensitizer capable of simultaneouslyabsorbing at least two photons and having a two-photon absorptioncross-section of greater than about 50×10⁻⁵⁰ cm⁴ sec/photon; and atleast one electron donor compound different from the multiphotonphotosensitizer, wherein the oxidation potential of the electron donoris greater than zero and less than or equal to that ofp-dimethoxybenzene; and at least one photoinitiator selected from thegroup consisting of aryliodonium salts, chloromethylated triazines, and2,4,5-triphenylimidazolyl dimers.
 32. The method of claim 31 wherein themultiphoton photosensitizer is capable of photosensitizing2-methyl-4,6-bis(trichloromethyl)-s-triazine when exposed in thewavelength range of the single-photon absorption spectrum of thephotosensitizer under conditions wherein no measurable multiphotonabsorption occurs.
 33. The method of claim 31 wherein the multiphotonphotosensitizer has a two-photon absorption cross-section of greaterthan about 100×10⁻⁵⁰ cm⁴ sec/photon.
 34. The method of claim 31 whereinthe multiphoton photosensitizer has a two-photon absorptioncross-section of greater than about 150×10⁻⁵⁰ cm⁴ sec/photon.
 35. Themethod of claim 31 wherein the multiphoton photosensitizer has atwo-photon absorption cross-section of greater than about 200×10⁻⁵⁰ cm⁴sec/photon.